The date validator requires the existence of all year, month and day parts. So it can't be used in this case.
To solve our problem, we can use a combination of regexp and callback validators. The first validator is used to check if the input matches with a pattern of time (HH:mm, for example), and the second one for comparing the time.
In the callback method, we respectively compare the start and end time. If start time is earlier than the end one, we need to set the end time as valid by calling the updateStatus() method:
The example uses the verbose: false option and place the callback validator at the end of list of validators. It ensures that the time in the callback method already passes other validators, therefore it matches with the time pattern provided by the regexp validator