Two timepickers - set min in second from value in first

I have two timepickers, start and finish. How would I go about setting the minimum time of finish to whatever was selected in the first + 15min? I'm guessing this has something to do with onset but Im not sure where to begin It would be nice to have the reverse true - if you set a finish_time the max of start time cannot be more than the value of finish - 15min. Thanks in advance!

` $('#start_time').pickatime({
//format: 'h:i A', // Displayed and application format
formatSubmit: 'HH:i:00',
hiddenName: true,
interval: 15, // Interval between values (in minutes)
min: '3:00 AM', // Starting value
max: '6:00 PM', // Ending value
});

$('#finish_time').pickatime({
//format: 'h:i A', // Displayed and application format
formatSubmit: 'HH:i:00',
hiddenName: true,
interval: 15, // Interval between values (in minutes)
min: '3:00 AM', // Starting value
max: '6:00 PM' // Ending value

});`