changing ParseHumanDuration to support timestamp values too (#684)

pkg/resources/common/duration.go

@@ -6,11 +6,20 @@ import (
 	"time"
 )
 
-func ParseHumanReadableDuration(s string) (time.Duration, error) {
+// ParseTimestampOrHumanReadableDuration can do one of three things with an incoming string:
+// 1. Recognize it's an absolute timestamp and calculate a relative `time.Duration`
+// 2. Recognize it's a human-readable duration (like 3m) and convert to a relative `time.Duration`
+// 3. Return an error because it doesn't recognize the input
+func ParseTimestampOrHumanReadableDuration(s string) (time.Duration, error) {
 	var total time.Duration
 	var val int
 	var unit byte
 
+	parsedTime, err := time.Parse(time.RFC3339, s)
+	if err == nil {
+		return time.Since(parsedTime), nil
+	}
+
 	r := strings.NewReader(s)
 	for r.Len() > 0 {
 		if _, err := fmt.Fscanf(r, "%d%c", &val, &unit); err != nil {