Thanks. In this case, it was mechanical earlier in the day that caused the plane we were to take from ATL to be 90 mins late getting to ATL. Had the plane not had issues earlier in the day, the crew would not have timed out. 2 hours on the tarmac, and we were really close to the de icing pad. Not sure if this led to UA looking to put people on DL. Also, UA had cancelled most of their Saturday flights out of ATL according to the UC. Who knows. Again, thanks for all of the helpful info. UA ended up giving me a $250 voucher for my trouble.