Appointments+ custom duration

I was provided this code to add in mu-plugins that allows me to have 20 and 15 minutes appointments.

add_filter( 'app-time-min_time', function(){
return 5;
} );

But the time slots displays now as if the service duration was 5 minutes.

I have only one service provider, what I would like to achieve is, having services with 20 and 15 minutes.

So for example, if 1 hour time slot(12:00-1:00) is booked from a service, a 2nd appointment booked for a 25 minutes service, I want the third appointment booked for another 1 hour service to start at 1:25, not the normal 1 hour slot.