Bike times during training vs. race day

There's a lot that goes into it. Do you have to stop a lot on training rides for stop signs, red lights etc? Is there wind, is the road better or worse? Too many things to really say. Not to mention most people tend to just ride faster in races because they push themselves more.

You'll only know after you do it. Until then it's all guessing. Not estimated, it's guessing. If you guess wrong you'll get rather annoyed at yourself because you failed to live up to expectations that were not reasonable (wind, etc). Don't do it. Go do the best you can on race day and take it from there.

I don't have to stop but I have to slow down for two turns and the roads are bad.  It takes 36 minutes to do the hilly course. I am hoping I can do 30 minutes for the flat/downhill course. 

Just go ride. Then you'll know.

I agree that it is a guess because of the factors mentioned by others.
Also, your training shouldn't be as hard of efforts as your race will be, so that can have a large impact on it too.

All right, I'll throw in my 2 cents on this. It depends on how hard you went on your hilly course. If you went hard and are expecting/hoping to go 6 minutes faster you have your work cut out for you. I would guess that you could go faster by probably a few minutes but to go from 16.7 mph to 20 mph is a big jump. But who knows. Most of my training rides are done far below what I do when I have a race number on. Sometimes competition gives you an extra gear you did not know you had.

And hopefully you don't blow up on the run because of it .