Do I need to exit and re-enter Thailand before my tourist visa expires to get a work permit?

I'm a 64 year old American, living in Thailand since 1 October. I have a tourist visa until I can get a work permit and my understanding of "the rule," that I need to exit, then re-enter Thailand is on or near the 90-day expiration date of my current visa. I was told this by my landlord, who is also a manager at the hotel I stayed in the first couple weeks of Oct, and confirmed by an online travel site. Is this correct and will some of you please offer input ?