Due date and reminder are incorrect for time-only expressions like "in 36 hours"

[idpaterson]

The workflow's logic for due dates and reminders assumes that any time-only expression has no significant date component. While this makes sense for times like "3:30" it doesn't work for unit expressions that can overflow the current date like "in 36 hours". Currently these expressions are not handled correctly either for the due date or for the reminder.