13 hours is not such a big deal, I'd just do it. Remember you're getting paid for it. it's best to keep good karma among the team. Now if it was something that'd take you a week or more, then you could involve your manager and ask him if that's the best use of your time, especially if you don't agree with it.
However, you sound like you need leverage in your group. Here's how you get leverage: ask for forgiveness don't ask for permission. Add stuff to the program as you see fit, and tell the manager or your colleagues after the fact. Don't ask them: "Is it ok if I add feature X". Rather, just add features that you personally want in the program. If they get upset at a new feature or don't agree with, be ok to remove it. If they like it, keep it. Another way is to also take a task that they give you, and to go the "extra mile" and add alot of things they forgot to mention. What happens will be your manager will peg you as a "go-getter" and will start putting his trust in you, and your colleagues will start seeing you as the lead. And then when things like what you mention happen in the future you'll have more say because you're essentially the star of the team.