Not sure what the question would be but it concerns a time field.

First of all, forgive me if this is simple, I am six hours into this wonderful software, I am, as they say, a newbie! I am creating a quoting database for my comapny and I want a field that, for example, I want to enter how many hours I think a certian task woudl take. I don't want to enter a start and end time, I just want to enter the hours I think a task would take. I can do it in a number of ways. I can enter 3:30 whcich means 3 hours and thirty minutes or I can enter 3.5 which means the same thing. Is there a way to do that? I can't seem to findf anythoing like this in the docs of forum querstions.