The last time I did field stand by, I did it in my car in the parking lot. 25 minute walk from the lot to ops. T-shirt and shorts.
The crew desk was offended when they called at 3:59, when I told them it would take me about 30 minutes to get on the DH, that was leaving in about 10 minutes. Oh well. I was offended when they called at 3:59.
You are correct, none of that is defined.