Make a mental note of how long it took to clog. Next time clean it before that much time has gone by.
I guess they say... check any new stove after 30 days. That will give an idea of how long it'll go. Most people learn what their stove needs. Some each month, some 6 months, some will go a whole season.
NOTE! If you change the brand of coal you are using, check ash build up again. There can be a huge difference from one coal to another.