I have missed it for a few months, and man was the house all sorts of smoky.
If I wait too long, I use Simple Green to get some of the worst off. Rinse real good, then do self cleaning. If you don’t rinse, you’ll be coughing and feel like your lungs are burning, not fun.
That happened to my wife while we were cleaning up an apartment of ours as we were getting it ready to rent again. At least that one could be salvaged. She had another one in a unit she owns that was so bad it couldn’t be cleaned and had to get a new range.