MyBB Community Forums

is it possible to ban ppl for 12 hrs, etc

It is. Go to a user profile, click ban user.

You'll be redirected to the admin panel. From there, choose ban length. There are predefined values (1 day, etc). If you need custom values apart from these, you'll need some modification on MyBB as this isn't possible out of the box.

By default it is not possible, but you can code a simple plugin or even use something like Hooks to hook at functions_fetch_ban_times.

Nevermind the above post, you will need to modify the following code as even hooking won't allow you to select lower values than a day unit.
https://github.com/mybb/mybb/blob/1b2540...7704-L7717