I had a similar problem. It started out like u said, when i tried startin the car after it had been off for 5 min it wouldnt start, but if i waited it'd be fine. Then the problem changed, i eventually couldnt start it at all when it was hot out (aka: daytime) but it would start fine at night when it was cool. Long story short (not really), the problem i think u have is the main relay. U can either buy a new upgraded one, or do wat i did, take it out, open it up and resolder all the joints together. The directions
here should tell u pretty much everything u need to know. Of course, it may not be ur main relay, but i'm 90% sure thats the problem. Good Luck!