There is a good thread on tuD that I was a part of a little while ago. Here are some excerpts that I think are relevant:
Joan 10: I diligently changed them every three days for a long time but for about three or four years have been changing them once a week and they work just as well with no problems!
Bowie: I did do a 5-6 day change for a while till I saw a slight infection when I removed my old site once - now I’m scared to let it go any longer than 3 days
Timbeak48: I did four days for a while and I HAD noticed a drop off in effectiveness after three days.
rgcainmd: There’s no way I’d let my daughter go longer than 3 days. The risks of developing lipoatrophy or lipodystrophy are not risks I’m willing to take.
Rphil2: With two minor surgeries to correct site infections, I switch at 3 days no matter. I also switch if the site itches or stings. Those two gashing wounds were terrible. I would never ever want to repeat that. 3 and out all the time. It only takes one. The second was the result of the first.
mee: I change mine every 2 days. I use contact steel inset- I do notice a difference with better Bg and avoiding highs
Jen: I use Contact Detach steel needle sets and change them once a day. Sometimes I leave it two days, but often my blood sugar goes high on the second day. I also sometimes change it more than once a day if the site gets itchy or irritated at all or if blood sugars go high and won’t come down.
artwoman: I notice a slight upward trend in bg’s (or downward trend in insulin performance) after 3 days. So I try to change every three days.
Scott_Eric: I used to let my Silhouette sites run as long as possible when I was in university and have significant scar tissue on my lower abdomen from being an idiot.
jjm335: I was struggling to get 2 days out of a site with Apidra and switched to Humalog.
Dessito: I change my Medronic sets every 6-7-8 days since that is how long it usually takes me to empty a reservoir (1.8U). I use Novolog and do not observe any lower insulin action in the later days of a set compared to the first days. I also don’t have infections, occlusions, or other skin reactions.
Beacher: you may not experience signs of lipohypertrophy or other tissue effects until some time later.
Jaime7: I have to change mine every 2 days my body rejects it quite rapidly.