That and the playing conditions. I go through strings a lot faster on warm and humid days that make me sweat just sitting down.
Really depends on how pedantic you are with your strings as well. I know some guys who will play a string right up until it’s on the verge of snapping. I also know some guys who will change strings as soon as they lose their bounciness. Me, I change mine when they start to get really fuzzy.
My Yelets is my main throw since it is beat. I use a string every 3 days usually which is about 8 hrs of play. I use it until it frays. My other nice throws always have fresh string. When they get a little worn they go on the Yelets.
I think fat kitty string lasts the longest for me. Thin(er) string just doesnt cut it anymore now that I use phat kats. I change my string after around 2-3 hours of play. For 5a I change it after about 4 hours of play, and for 4a I like never change the string lol. I dont take 4a that seriously
i use kitty nylon 1.5 and i change it at least once a day. I play about 4 hours a day. I don’t really wash my string at all, ive never tried it. I should. But I mostly just change the string when the color is dulled (i mostly use neon yellow), when it starts getting fuzzy, and when it doesn’t hold its tension as well. If if twists a lot after like 2 throws then i know its time to change the string.
This is my routine, I change when they become a pain to maintain their tension. Once it gets to the point that I can’t do a suicide reliably after a few throws, it is time to go.