How to create Reservation Form with varying services availability

May I define services that are reflected properly on the calendar and reservation piece with varying work time required for each task so that when a client wants a job that takes 4 hours, he cannot take a 2 hour available spot for that job?

Just want to clarify your question about making a calendar with your customized value. You wanted to put your own value on calendar is that what you are trying to do? I was looking for all the dates and calendar widgets that we have but unfortunately I didn't find any widgets that dates can be modified with your own values. Dates are set as numbers and they have fix values.

About the reservation form we have a Appointment Slot widget that you can try together with our Dates or calendar widgets. Please clarify if this is not what you are up to.

While searching I found our booking form. I think this is what you are looking for http://bookings.jotform.io/. Also check this sample created by my colleague https://shots.jotform.com/elton/book/