If you did a cut lap setup while glassing the bottom, you’ll need to let the board set until it’s just barely tacky. How long that takes is completely dependent on your resin and the environmental conditions. For me it’s usually in the 4-6 hour wait time. When the board is set enough to handle you’ll need to flip it over to do the cut lap. One word on that though:
DO NOT TOUCH THE BOARD WITH BARE SKIN!
Until you apply the hot coat, you can’t touch the board unless you are wearing gloves. Getting body oils on the board will cause your hot coat to fish eye and that is no fun. The best thing to do is treat the board like it’s radioactive until then.
To start with the cut lap, take a razor blade and cut along your tape line at the nose and tail. It may be difficult to get in there, if it is, I’ve found that starting from the area that isn’t glassed along the stringer and splitting the glass down to the tape line helps give you something to get started with. Now you can start to work your way down the rail. Keep the razor flat against the board on the rail side, lift up the tape with one hand and cut it with the other. Pull the razor like a zipper down the line.
Inevitably, this process will tear up some foam and mess with your paint job. This is the reason why surfboards have pin stripes. It’s how you hide your crimes. I’ve done a pinstripe and I’ve fixed up the paint and I kinda prefer fixing up the paint.
The worst damage 
Fixed, but I shouldn’t have free-handed it
Next you’ll need to sand down the areas where you overlapped the darts you made. This is why you want to check the overlap and trim as much as you feel comfortable with. This board actually had pretty good seams but they still needed sanding.
Before 
After
You’ll also need to sand out all those drips on the rails. Preventing this is something I need to work on. It seems that no matter how long I work it and try to remove as much excess as I can, while it sets drips still form.
Drips 
Drips sanded out
One last thing to do is to press down the edge of the glass. You want to get it flush with the foam.
From here, the steps are the same as glassing the bottom. You’ll still want to tape up the bottom for the cut lap from the deck.