I echo exactly what Run4pancakes said. I am a 3-4 day changer too. I don't get itchy, never have leaks and my wafers don't significantly start peeling off, so there are really no obvious signs of when to change for me. My issue was eroding of the wafer (and Eakin ring) right up against my stoma so that stool was ending up contacting my skin there if I went longer than four days. I knew because when I went 5 days, my skin started to get really red right around my stoma. When I go 3 or 4, it looks great.
Of course, if you peel your wafers off too often, that can irritate your skin too. Still, when I had a wound vac on, I had to change my wafers every other day and I still didn't get that much irritation from ripping them off so often. During this time, I did switch to standard wear instead of extended wear, which were easier to peel off when I wasn't leaving them on for very long.
-39 years old
-Officially diagnosed with UC in 2006, though had symptoms since 1999.
-Had mild/moderate symptoms continuously until severe flare in autumn 2010 which required 2-week hospital stay
-Took Asacol, Rowasa, Canasa and Prednisone to manage flares but meds stopped working
-Tried 1 dose of Remicade but had excruciating joint pain and discontinued
-Had permanent ileostomy surgery 11/8/2010