car won't start after it has been runninf and then cut off

I have this same problem on my Saturn. It starts right away in the morning and right away after work. But if I run an errand, the car will start - I get to my destination - I get back in after my quick run - and the car does not turn over. I wait 30 or more minutes before it turns over....just like nothing was wrong with it in the first place. Like a cooling period. Battery is good, cables good, car runs smooth when it is turned over and running....I'm at a loss....I've a Saturn SC2 1997. 4 cylinder. Can someone answer why this is?

This can be leaking injectors. Check your injectors