after recently getting some tips on here about string tension ive gone 4 days without replacing the same string. Every not i have been able to get out and the string tension itself is staying good. How about you? how long have you gone without having to change a string because of a knot you cant get out or anything like that.
I’m not really up on when you should change strings, but i’ve had the same one on my Dv888 for over a month now. It works perfect for me. Holds suicides great and whips just fine. ;D
I’ve gone months of decent play, but not a super ton. Also, I can get any knot out. I can almost guarantee it. 
I use G-string so I always undo the knot no matter what. I’ve gone 2 months with one piece or G-string Intentus.
I usually wear out the string after about an hour of play.
I’ve been using one Highlight on multiple yoyos since SoCal, which was over a month ago.
I have this mystery experimental yoyo string a friend gave me lol so I haven’t been changing that, bout 3 days now =0 but no end in sight (I know 3 is lame but it’s nylon so it seems sturdy).
I use 50/50, so I only have to change it when I get a knot ( about every hour or so )
You can take the knot out. Use pliers.
I don’t think that you can create a general rule for changing the string! It depends on many factors. On some of my Yo’s the strings are in for 5 days and more and on some others (especially on my favorites) I change the string nearly every day.
If you seek the risk, you can use the strings as long as you want, but I can tell you that you should’nt underestimate the holes in your wall caused by a fullmetal Yo! 