Title says it all:)
everyday
When it gets well…
Icky. 
Usually twice a week.
Whenever I feel like I should change it… could be a couple days or it could be a month
Depends on the string. Reg poly, every hr or so. Toxics wash after a week and have another week. Kittys usually every day.
It follows a strange pattern for me. I mainly use toxics but I could go on one string for a single hour, or up to ten hours…
once a day. i primarily use kitty string or snacktime string
if im using something a bit more durable, obviously a little longer 
Depends on the string. The dragon string can last for months and gets better with age. But it has a very unique feel and almost no bounce, so it depends on what you like, others may change it after it looses its initial small bit of bounce.
I like the kitty string bounce so I change it often when I’m paying it, perfect being it comes in large bulk, it definitely has a specific place in my string use collection.
Twisted usually lasts me a couple of weeks after break in depending on the type and how I want to be throwing. The twisted could really be played forever like the dragon, it just depends on how you want it to feel (talking type B, A, A1) as it continues to change after break in.
Also Stringlab, I’d say around a week to a few days. Like the kitty, I play these for the bounce quality.
Sniffy-Yo.com
@Sniffyo on twitter
I change my string depending on what type it is and how I feel that day. What happens is when I change my string, I throw it in my case. So even if it isn’t used thoroughly, I still have it. Then if one day I think, “Oh I would love a Hamstring right now,” then I just find one and see if it satisfies me. If it is too used, I will just toss it.
But generally, I would use my Hamstrings for about 2-4 days, Toxics for a week or so, and my specialty strings I got from a guy named Chris for about 1 day, Regular poly for a day, Kevlar for a LONG time, and my own Big Yoyo strings for about 3 days (the type with the bounce), or about 5 days for the type that is similar to a toxic string.
I use nylon string wich is pretty strong, so i change it about once every week.
I change once every month/2 months. More if im preparing for a contest.
About once every 6 weeks?
DRAGON.
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I sometimes change sooner if I feel like it, but that’s about the same for me with Type X.
Really depends on the string. For the past year I used polys, and I would change out every 2 days. That was just playing for fun. Preparing for competitions I would change like every half hour or and hour. Right now I’m using slick 6 50/50s and I change every 2 hours of play time.
I will go through a hundred a week when I am practicing for worlds. Sometimes more.
Haven’t changed a string in weeks. Just change yoyos. I’ve yet to change a dragon string. And kitty string about 3 days unless I’ve got dirty hands.
For most of my yoyos I usually change the string about once a week.
Daily.
I yoyo alot and change like every two weeks I use yyn highlights i prefer a well broken in string