Upon return to Chiang Mai from overseas, your tenant has to go to Immigration by 4pm the next day (note, calendar day not working day) with his passport and the TM30 acknowledgment slip which you will be getting when you make the initial report and tell the counter that he is there for an update. No new TM30 report is required.
No new TM30 if no change in address. Just bring your passport with the new TM6 and prior TM30 receipt to Chiangmai Immigration by the next day. TM30 submission/update is available EVERY day, 0830-1600 hrs, even for announced office closures. Just went today.
When and what you need to do depends on the Immigration office you report to. Some do not require re-reporting for domestic travel, some do. Some require a new TM30 when you travel overseas, some only require you to drop in to let them update the new arrival card (TM6) number to your previous TM30 record. Suggest you check with the office that you report to.
Don’t think there is any requirement how long you need to stay in Thailand. Rather, the country you are exiting from and returning to will determine how long you need to be out.