What do you think if this line appears at the bottom:
"All time are GMT +2".
I think this is a multi-timezone forum, so...

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! :)

And, what about choose timezone in profile?

I already explained - most of users don't know what that's and most often never change. So why then would we need to spend resources for it?
It appears only your own wish. If you would like the custom add-on like this, it's possible to program.

Sorry to dig this post up, but I would think that the forums are mostly used in conjunction with a bigger site. Being able to use the same timezone in the forums as the whole site is using would be convenient.

An example would be a site for an online game, where the game time (and thus the 'site' time) for game events would be in GMT, but minibb uses GMT -5 because that's the timezone that the server's located in.

As you said, Paul, it would be easy to implement a custom add-on for this, but don't write off this suggestion as useless except for one or two users.

I'm not sure why do you need add-on for that.
miniBB already contains time shifting option, which is under setup_options.php - $timeDiff.
Read manual on how to set up this option.

This thread is not about shifting the time, but displaying the time, which I'm sure won't bring any fantastic results to your profits or visitors, that's why I'm not interested to develop it even for free.