A lot depends on the quality of the chain, type of wood and how much dirt the chain sees.
I have my best luck with Stihl brand chain, on one saw that only cuts 'clean' wood, the chain can last months, on a saw that's felling trees or working close to the ground, where it's likely that there's some dirt or sand in the bark or when cutting hardwood, the blade can last considerably less time. I have both a portable sharpener, as well as an electric sharpener from Harbor Freight. The HF sharpener works fine but I find that I only use that for major resharpening jobs, I can use the portable to touch up a chain that's not real bad.
I also have 10 or 12 spare chains for each saw, and all are kept sharp and ready to use so when working, all I need to do is swap out the chain if one fails to cut properly or gets dull.