MoonShadows said
I don't have any experience with new strings except the ones that came with my Fiddlershop Concert Violin when I purchased it two months ago. I'll have those for a while.

I was just reading on the internet last night that professionals usually change their strings every six months (I imagine some do it more often), and for the rest of us, we should change them every year. Enjoy the new strings...and the sound!  

For that matter, even many amateurs change their strings every six months if they practice and perform enough. A professional who performs a little and mostly teaches will probably go six months on a set of strings too, but those who perform regularly may change their strings much more frequently, depending of course on how much they practice and perform. I've heard of players in the major orchestras (who rehearse daily and perform up to 150 concerts a year) changing their strings as often as every 3-4 weeks.

Depending on the brand, you can expect synthetic strings to be good for 100-150 hours of playing before they start to sound noticeably duller. After that, they're still usable for many more hours (I've gone well over 200 hours on a set of strings and there was still no sign of unraveling) but you'll hear a huge difference when you replace them.

It's a fairly common practice to replace strings after that 100-150 hours, so that they're still usable as backups in case a string breaks. If you need a string to perform on immediately, it's better to use an old string that sounds a bit dull but is already broken in and stays in tune than to use a brand-new string that goes out of tune.

I don't clock my time. I just estimate that I play 5-6 hours a week on average, taking a few weeks off each year, which works out to changing strings about twice a year.