It’s normal that the progress bar starts at 0 again and goes through the 48,000 first steps while doing nothing, this is done to get at the same point in your data that you were at the time of checkpoint.
If it takes 5 hours to get there, the cause is very likely that your data loading is too slow, because this is the only thing the Trainer does for those steps (no model update, no evaluation, no logging, no saving, just going through the batches).