There's no problem to develop this add-on for you, if you need it. I think it would not even go over 20 bucks :)
But for default version, I think, it's not important what timezone the forum is in. Most of users are local and this co-exists with the forum local time. For miniBB forum, time zone doesn't matter, because users are coming from all over the world, and for them, information is important, not actually the minutes and hours when it was posted; only day of the year may matter, but it doesn't really depend on timezone.
Also, I think, most of users don't actually know, what the term "time zone" means. GMT +2 - that may look scary for them! :)