Trouble starting at times! I need some help!

My girlfriend has a 1991 Acura Integra with 189,000 miles on it. She goes to work at 7:30 in the morning, and it starts fine. She parks it when she gets there. She'll go on lunch and drive. But when she leaves at 4:30pm. It won't start. It sounds like it wants to. You turn the key and ya get the startin sound, but just won't start!

But when I go to look at it at night about 9:30pm. It starts fine.? It's driving me crazy!

I've had a few thoughts.
one being maybe something to do with the battery, or maybe the "starter sylanoid" I beleive in these engines, the starter and sylanoid are together.
or maybe something with the spark plugs and the 100 degree weather we've been havin?

I would really greatly appreciate any info anybody can give me on this issue!