I've had a few instances of the gel wrinkling in this way... In my case I'm almost certain it's when the paint on the buck isn't good quality and reacts.
Must say I've not used 2 layers of gel coat on any of my moulds as I've been worried about the second coat attacking the first and it's hard to judge when it's cured enough.... Is it better to leave it a couple of days and then key it up?
On a side not, I have made some very successful moulds in a single day... Most significant is my front clip that I needed to use at 8pm (meaning demould deadline of 6pm) and had a delay of material deliver meaning I couldn't start the final section till midday... I increased the catalyst a large amount to make it go quickly and fortunately it came out good rather than being ruined.