Again, I am not an expert but I don't think your ramp up/down time should be taken away from the cureing time. You still need 10 hours at 100c.

Brian.

I'm possibly not the best person to comment as I haven't personally used pre-preg before, but from what I understand, your ramp rate could still be an issue. Ideally you want to ramp temperature up at 1-2 degrees per minute. What oven are you using, just a household one? They won't have the precise temperature control really needed for pre-preg, they are designed to heat up quite quickly. Otherwise, are you leaving your vacuum pump connected for the duration of the cure? Or are you disconnecting it? You may find if you are disconnecting it that you either have a small leak in your bag or you are getting outgassing of solvents that are reducing your vacuum and affecting the finish. 

Hello to all, I'm still at a very early learning stage with composites , but would grateful of some professional advice or guidance to help me along the way.