diff --git a/core/cron.go b/core/cron.go
index 4287093..e6a017a 100644
--- a/core/cron.go
+++ b/core/cron.go
@@ -8,57 +8,95 @@ import (
 	"time"
 )
 
+type cronSpec interface {
+	// Get the next time matching this spec that is after the base time.
+	GetNextTime(base time.Time) (nextUpdate time.Time)
+}
+
 func GetNextSpecTime(lastUpdated time.Time, spec string) (nextUpdate time.Time, err error) {
-	var nextUpdates []time.Time
-	switch {
-	case strings.HasPrefix(spec, "every "):
-		nextUpdates, err = parseEverySpec(lastUpdated, spec[len("every "):])
-	case strings.HasPrefix(spec, "at "):
-		nextUpdates, err = parseAtSpec(lastUpdated, spec[len("at "):])
-	case strings.HasPrefix(spec, "on "):
-		nextUpdates, err = parseOnSpec(lastUpdated, spec[len("on "):])
-	default:
-		// "HH:MM" is implicitly an at-spec "at HH:MM", so see if it's that
-		nextUpdates, err = parseAtSpec(lastUpdated, spec)
-		if err != nil {
-			return time.Time{}, fmt.Errorf("unknown spec format: %v", spec)
-		}
-	}
+	var cron cronSpec
+	cron, err = ParseCronSpec(spec)
 	if err != nil {
 		return time.Time{}, err
 	}
+	return cron.GetNextTime(lastUpdated), nil
+}
+
+func ParseCronSpec(spec string) (cron cronSpec, err error) {
+	switch {
+	case strings.HasPrefix(spec, "every "):
+		cron, err = parseEverySpec(spec[len("every "):])
+	case strings.HasPrefix(spec, "at "):
+		cron, err = parseAtSpec(spec[len("at "):])
+	case strings.HasPrefix(spec, "on "):
+		cron, err = parseOnSpec(spec[len("on "):])
+	default:
+		// Interpret "HH:MM" as "at HH:MM"
+		cron, err = parseAtSpec(spec)
+		if err != nil {
+			return nil, fmt.Errorf("unknown spec format: %v", spec)
+		}
+	}
+	return
+}
+
+// Return the time that follows the base time most closely.
+func nextAfter(base time.Time, nextUpdates []time.Time) (nextUpdate time.Time) {
 	for _, next := range nextUpdates {
-		if next.After(lastUpdated) && (nextUpdate.IsZero() || next.Before(nextUpdate)) {
+		if next.After(base) && (nextUpdate.IsZero() || next.Before(nextUpdate)) {
 			nextUpdate = next
 		}
 	}
 	return
 }
 
-// Get the next instance of the every-spec after the base time.
-// An every-spec is a Go duration string.
-func parseEverySpec(base time.Time, everySpec string) (nextUpdates []time.Time, err error) {
-	var duration time.Duration
-	duration, err = time.ParseDuration(everySpec)
-	if err == nil {
-		next := base.Round(duration)
-		if !next.After(base) {
-			next = next.Add(duration)
-		}
-		nextUpdates = []time.Time{next}
-	}
-	return
+// An every-spec is a Go duration string, e.g. "every 5m"
+type everySpec struct {
+	duration time.Duration
+}
+
+func parseEverySpec(spec string) (*everySpec, error) {
+	duration, err := time.ParseDuration(spec)
+	if err != nil {
+		return nil, err
+	}
+	return &everySpec{duration}, nil
+}
+
+// Get the next time matching the every-spec that is after the base time.
+func (spec *everySpec) GetNextTime(base time.Time) (nextUpdate time.Time) {
+	next := base.Round(spec.duration)
+	if !next.After(base) {
+		next = next.Add(spec.duration)
+	}
+	return next
 }
 
-// Get the next instances of the at-spec times after the base time.
 // An at-spec is in the patterm HH:MM[,HH:MM,[...]].
-func parseAtSpec(base time.Time, atSpec string) (nextUpdates []time.Time, err error) {
-	for _, timeSpec := range strings.Split(atSpec, ",") {
+type atSpec struct {
+	hours   []int
+	minutes []int
+}
+
+func parseAtSpec(spec string) (*atSpec, error) {
+	var hours, minutes []int
+	for _, timeSpec := range strings.Split(spec, ",") {
 		var hour, minute int
-		_, err = fmt.Sscanf(timeSpec, "%d:%d", &hour, &minute)
+		_, err := fmt.Sscanf(timeSpec, "%d:%d", &hour, &minute)
 		if err != nil {
-			return nil, fmt.Errorf("could not parse %s: %v", timeSpec, err)
+			return nil, fmt.Errorf("could not parse at-spec %s: %w", timeSpec, err)
 		}
+		hours = append(hours, hour)
+		minutes = append(minutes, minute)
+	}
+	return &atSpec{hours, minutes}, nil
+}
+
+// Get the next time matching the at-spec that is after the base time.
+func (spec *atSpec) GetNextTime(base time.Time) (nextUpdate time.Time) {
+	nextUpdates := []time.Time{}
+	for i, hour := range spec.hours {
+		minute := spec.minutes[i]
 		// The time instance on the same day as the base time
 		specOfDay := time.Date(base.Year(), base.Month(), base.Day(), hour, minute, 0, 0, base.Location())
 		// Bump it forward one day if it's before the base time
@@ -67,7 +105,7 @@ func parseAtSpec(base time.Time, atSpec string) (nextUpdates []time.Time, err er
 		}
 		nextUpdates = append(nextUpdates, specOfDay)
 	}
-	return
+	return nextAfter(base, nextUpdates)
 }
 
 var weekdays = map[string]time.Weekday{
@@ -131,62 +169,66 @@ func (date *onSpecMonthDay) getDates(base time.Time) (dates []ymd) {
 	return
 }
 
-// Get the next instances of the on-spec times after the base time.
 // An on-spec is in the pattern DOW[,DOW[...]] where DOW is an abbreviated weekday
 // or M/D[,M/D[...]] where M/D is a month and day.
 // As a special case, "*/N" matches the Nth day of every month.
 // An on-spec may be followed by an at-spec; otherwise, "at 00:00" is implied.
-func parseOnSpec(base time.Time, onSpec string) (nextUpdates []time.Time, err error) {
-	type Time struct {
-		Hour   int
-		Minute int
+type onSpec struct {
+	atSpec atSpec
+	dates  []onSpecDate
+}
+
+func parseOnSpec(spec string) (*onSpec, error) {
+	atPart := "00:00"
+	if at := strings.Index(spec, " at "); at > -1 {
+		atPart = spec[at+len(" at "):]
+		spec = spec[:at]
+	}
+	atSpec, err := parseAtSpec(atPart)
+	if err != nil {
+		return nil, fmt.Errorf("could not parse at-spec %v: %w", atSpec, err)
 	}
 
-	atSpec := "00:00"
-	if on := strings.Index(onSpec, " at "); on > -1 {
-		atSpec = onSpec[on+len(" at "):]
-		onSpec = onSpec[:on]
-	}
-	var atTimes []Time
-	for _, timeSpec := range strings.Split(atSpec, ",") {
-		var hour, minute int
-		_, err := fmt.Sscanf(timeSpec, "%d:%d", &hour, &minute)
-		if err != nil {
-			return nil, fmt.Errorf("could not parse at-spec %s: %v", timeSpec, err)
-		}
-		atTimes = append(atTimes, Time{hour, minute})
-	}
-
-	var dates []ymd
-	for _, daySpec := range strings.Split(onSpec, ",") {
-		var date onSpecDate
+	var dates []onSpecDate
+	for _, daySpec := range strings.Split(spec, ",") {
 		if weekday, ok := weekdays[daySpec]; ok {
-			date = &onSpecWeekday{weekday}
+			dates = append(dates, &onSpecWeekday{weekday})
 		} else if strings.HasPrefix(daySpec, "*/") {
 			var day int
 			_, err := fmt.Sscanf(daySpec, "*/%d", &day)
 			if err != nil {
 				return nil, fmt.Errorf("could not parse month/day %s: %v", daySpec, err)
 			}
-			date = &onSpecEveryMonth{day}
+			dates = append(dates, &onSpecEveryMonth{day})
 		} else {
 			var month, day int
 			_, err := fmt.Sscanf(daySpec, "%d/%d", &month, &day)
 			if err != nil {
 				return nil, fmt.Errorf("could not parse month/day %s: %v", daySpec, err)
 			}
-			date = &onSpecMonthDay{month, day}
+			dates = append(dates, &onSpecMonthDay{month, day})
 		}
+	}
+	return &onSpec{*atSpec, dates}, nil
+}
+
+// Get the next time matching the on-spec that is after the base time.
+func (spec *onSpec) GetNextTime(base time.Time) (nextUpdate time.Time) {
+	// Convert each type of on-spec date spec to a concrete YMD date
+	var dates []ymd
+	for _, date := range spec.dates {
 		dates = append(dates, date.getDates(base)...)
 	}
 
-	// Now, for each date, create a datetime based on the at-spec.
+	// Then, for each date, create a datetime for each at-spec.
+	nextUpdates := []time.Time{}
 	for _, date := range dates {
-		for _, atTime := range atTimes {
-			nextUpdates = append(nextUpdates, time.Date(date.Year, date.Month, date.Day, atTime.Hour, atTime.Minute, 0, 0, base.Location()))
+		for i, atHour := range spec.atSpec.hours {
+			atMinute := spec.atSpec.minutes[i]
+			nextUpdates = append(nextUpdates, time.Date(date.Year, date.Month, date.Day, atHour, atMinute, 0, 0, base.Location()))
 		}
 	}
-	return
+	return nextAfter(base, nextUpdates)
 }
 
 type Schedule struct {