In article ,
"RST Engineering" wrote:

Jim, I haven't looked up the part 121 rules since I left the airlines, but
as I recall, the "duty time" is defined as flight time. No limit on how
long a crewmember can sit idling on the ground. Last I looked it was 8
hours a 24 hour day, 40 hours in a 7 day week, 100 hours in any 30 day
period ("month") and 1000 hours in a calendar year. Perhaps that has
changed.

As I was recently told, the crew clock doesn't start until the first
engine is started.