Can I extend my Visa exemption stamp in Chiang Mai just 2 days after receiving it?

Is it possible to extend a Visa exemption stamp in Chiang Mai just 2 days after getting it?

I will fly into Chiang Mai, where it's relatively easy and fast to extend. After that I'll move to the islands where immigration offices are much harder to reach. So I'd rather extend while still in Chiang Mai but I'm not sure about the minimum time left before one can do so.