Every plan includes daily talk time for Quest Calls: 20 minutes a day on Basic (free), 2.5 hours on Pro, 7 hours on Ultimate. It resets at midnight UTC, early morning in the UK.
The clock only runs while you are both in the call, so waiting alone for your match costs you nothing. When your time runs low during a call, a banner with a countdown appears a few minutes before the end. And a call only ends for time when both of you are out of time; if your match still has some left, the call keeps going for both of you.
If you upgrade during a call, the call continues on your new allowance.