There is a different construction for that though. Just like there's 'They will be playing' and 'They will play' in English, both valid, both similar meanings, but there are different constructions in Gaelic for each of those. See joannejoanne12's post.
Why not are playing... Or are going to play... ? Are these answers just completely wrong? From the gaelic examples I'm getting this use of bidh to bi for habitual actions or timetabled future events. I think the use of will here is different.
If a specific time or date that's singular is used, (such as tomorrow) then treat it as future tense. If it's something that can be a regular thing (like mornings in general, or mondays) then you can translate it as the habitual present.