I just have a general question about the resume process, how would they know if you actually volunteered the amount of time you said. Is it necessary to have and tangible evidence or do they just take your word for it?
In general, they take your word for it, but if they have any reason to believe you might be, they can always try to verify it by calling the organizations you say you volunteered for. Alternatively, they can also ask you about your experiences doing X in an interview, and they can usually smell BS answers.
In summary, don't lie about anything on your app; if you lie and it works, it might help you a little bit, but if it comes out, you're screwed.
A good logical thinker can pick something like this out. If you have a job and work 20 hours a week, that gives you very little time to do other stuff besides classes. If you said you volunteered on average of 5 hours a week, you would be ok. If you said you volunteered on average of 10 to 20 hours a week, I would check on it.
Just be honest. The truth is, and it shouldn't be shocking, a good high percentage of applicants to any graduate school "up" their EC stuff from what the truth is.