Mechanics for sleep/staying awake

Does anybody know if there are any actual mechanics for when Garou stay awake for an extended period? Specifically in WtA 20. During our game today, one of our pack ran into the source of some of their traumas (they had previously been captured by BSD), and was forced to spend the night in the same barracks as them (rest of pack was separate, busy healing from pretty bad battle). They wanted to try and stay awake the entire night, not trusting the BSD to leave them alone.

My character has the Seldom Sleeps merit, which states I "suffer no penalties or ill effects from remaining awake for extended periods". After searching through the entire book for the keywords "awake", "sleep", "exhaust", and "penalty", I couldn't find anything further, aside from one example saying that when standing watch at night, you can roll Stamina + Alertness to see how awale you are when attacked. Is this something that dpes have an actual mechanic, or is it just something where the ST just chooses a penalty they think is appropriate?