_reminder_minutes matched the offset with (?:m|min|minute|minutes)\b and
(?:h|hr|hour|hours)\b. The trailing \b makes the common plural
abbreviations "mins"/"hrs" fail to match (after "min" the "s" is a word
char, so no boundary), so reminder_minutes "5 mins" or "2 hrs" returned
None and the event was created with no reminder, silently.
Widen the two unit regexes and the matching reminder_only description
regex to a strict superset that also accepts mins/hrs. The sibling
duration parser already accepts these forms (it has no \b), so this only
brings the reminder parser in line.
Ashvin