Free Play Time can be won through events. It's activated as soon as you claim it.

While active, the coin or token cost for puzzles is removed. Once you've unlocked a free puzzle, it must be finished before you can unlock the next.

When you select a puzzle to unlock, you'll see how many free puzzles you have remaining. Once the limit is reached, free play time will end and the timer will disappear (shown over the token counter).

You cannot use this reward to unlock puzzles in the pack for the currently active event (these are unlocked with the puzzle rewards instead).

You can activate more than one at a time (the times will add together). 

Remember to claim all your event rewards before the end of the event!