Most airlines and airports recommend 1.5-2 hours for a domestic flight - roughly the time it takes without immigration/exit control, which most domestic routes don't have, and typically shorter bag-drop and gate cutoffs than international flights.
The same factors as international flights - time of day, airport, and checked bags - still apply, just without the immigration segment. A domestic departure from a very busy hub at peak time can still take longer than a quiet international one.
These are general, statistically-modelled estimates - not a guarantee. Always allow extra time for anything unusual, and check your airline's and airport's own current guidance.