Potions and certain items grant benefits like enhancing smithing or having increased health generation for a certain duration. How is this time measured? Is this clock time or in-game time? Does time spent in menus count against the given time?
The duration for effects are all measured in clock time1. The game time, by default, is set to a scale of 20, so 1 minute in real time is equivalent to 20 minutes in game time.
This other question explains exactly what actions freeze the game time.
1Waiting and fast travel, despite not advancing much clock time, does count against the durations.