an example of this is during weather issues...
I was on a DEN-SJC back in april. Pushed back at 615p. Online recorded 615p as actual departure.....we were stuck on the tarmac waiting in line to get de-iced...didn't get to SJC until past 11p.

online...it showed.... actual departure 615p, actual arrive 11pm...can you imagine a 5 hour flight between DEN and SJC ?