Today there is a difference between squadron and tactical callsigns. Squadron callsigns rarely change, squadron callsigns are used for training and talking with controllers (ATC, FACSFAC, Range, etc). Tactical callsigns are used on actual real-world missions and do change. I don't know how often. During super major exercises here in FL I do not think the tactical callsign changes daily. During our last big aircraft carrier exercise the same tactical calls were used several days before changed.
I lived here in FL many years then moved, now back in FL FANG and SNAKE were always FANG and SNAKE and still are FANG and SNAKE as are a bunch of calls still the same after 10+ years. And SAM29000 / Air Force One has been SAM29000 / Air Force One since day one.