Can appendicites take weeks or months to actually feel the strong pain or that's rare ? & everything always happens it 12-24 hours ?

Chronic appendicitis: Yes, on occasion, appendicitis is indolent, and can persist without rupture for weeks or months. This is not the usual presentation, which can progress to rupture in 18-48 hours. Just this week we had a patient with a month long presentation, without ever rupturing. Typically, appendicitis presents with peri-umbilical pain, loss of appetite, pain then radiates to rlq. Hope this helps. Good luck.