[AccessD] A2K: This should be easy

Hello all
This should be simple.

I have a control on a form (txtStartTime). Formatted for Short time (i.e.
hh:mm)
I want to take say...5, 10 or 15 minutes from whatever time is in
txtStartTime

So take away 15 from 11:00 should give me 10:45

How do I do this.

<Sigh> this should be easy. It probably is, I'm just brain fading.

Darren