Playtime rewards are rewards that can be claimed once you have played for the goal amount of hours. The hours are counted from the time you are connected to the server. It does not come from how long steam says you have had the game running.
You don't need to be actively playing, you can be afk and dead. A toilet will help refill your hunger & thirst to prevent death. If in a snow area you will want some heat. Playtime rewards reset weekly midnight est time the day before your usual wipe day at the daily refresh.