I doubt that they actually check into it, but it might come up in an interview. So if you said that you spent 300 hours volunteering in a soup kitchen, they might ask you about the type of experiences you had. If you can't answer the question very well they might be suspicious.
I also ran into this problem on my app. In high school I volunteered with the local ski patrol for 3 years. I spent at least 8 hours almost every weekend each winter (along with some summer stuff, like helping out at bike races). I don't remember exactly how many hours I put in, so I said "200+." I probably did many more hours than that, but I didn't want to overstate my hours. If it comes up, I'll talk about specific things that I did/tell a funny story or two.
