I am not an adcom, so I may not be providing the most informed opinion. Here is what I think, though. 25 hours of volunteering would definitely be cause for concern. Many of the people applying have decent stats, so it is things like a dedication to service that makes people stand out. Not everyone with a 3.7/30 gets accepted. I don't know what the rest of your activities look like, but I would recommend more volunteer hours. Find something that you are passionate about and that will give you the motivation to continue doing it. It's not so much about the number of hours as much as it is about what you got out of it and how it made you grow as a person. This is why it is important to do something you find meaningful. Even with that said, I think that there is a minimum amount of hours that will show adcoms that you have a desire to serve others. Pick a few things that will show longitudinal commitment rather than lots of short-term activities.
