Check the next billing day & Cancel PRO subscription

Open Google Play Store app.

Click your account.

Then follow below.

Also you can know when is the next payment in this page.

Yes, you can cancel your subscription!

If I join at 25th for the monthly plan, do I still can use PRO for a month?

Definitely, YES! If you join at 25th & even if you unsubscribe it, at least you can still use until 24th of next month.