You must work

Hi,

Please check my synthesis.

You must work for three hours. After that you can play.
a) You must work for three hours before you can play.
b) You must work three hours and then you can play.

You must work for three hours. After that you can play.
a) You must work for three hours before you can play.
b) You must work for three hours and then you can play.

‘For’ in (b) isn’t altogether a requirement.

Alan / Beeesneees,
“You must study three hours and then you can play.”
Is this sentence OK?
Can I leave ‘for’ after the verb - study?
Thanks.

There’s no point in asking a question that we’ve both already given our opinion on.