How does AA interpret the reserve rule on "reasonably available by ground transportation"? Is there a time frame, or does it vary based on event and/or individual pilot?
No time frame set in writing.
The only time I've heard guys getting noticed is pulling Reserve using a "reasonably available" standard that is beyond ridiculous, DEN to ORD or ATL to MIA. What will usually set off the trip wire in those cases are another junior guy getting screwed into flying the other guys trip and complaining to the Chief's.
3 hours from the closest airport of EWR, JFK or LGA probably won't flag you. The Chiefs know NYC/MIA/LAX traffic. I've heard of Vero Beach, Naples, Ft Myers to Miami. TPA might be pushing it. One could probably live in LAS or PHX and have quicker show times than living in some areas of L.A.