I think there have been a few Adventure time subs, but they're usually mash-ups. Like this:

I am thinking in a mush-up with megaman, but I don´t know if call it Adventure Time, or MegaAdventure or something like that. I want to call it just Adventure Time, but I don´t know if I can use the name

My bet is that you can't. I guess Mega-adventure, Megatime or adventureman would be acceptable because it's clearly a parody. But an American should verify this.

thanks!! (y)

I think Poeha is right on that. Maybe Peanuts Time or something like that. The design itself says all that needs to be said so as long as you're nudging people in the right direction with the title it's not a big deal.