Unfortunately he has the right to entry as long as he provides the proper notice. Arguments alone will not be sufficient to prevent him from entering the dwelling. Unless he imposes some sort of danger or threat, there is not much you can do.
Maybe there is more you aren't including, but based on the facts above, your remedies are limited.
Under the law, 24 hours is presumed to be reasonable unless there is evidence to the contrary. You being away for surgery and leaving your minor children at home is evidence that 24 hours is NOT contrary. (California Code of Civil Procedure 1954(d).
I would let the landlord know that normally 24 hours is OK, but not in this instance because you are having a medical procedure.
Also, the notice must be made in writing and include the date, approximate time, and reason for the entry. If he didn't do that, then the notice is not valid.