I string them every 6-7 weeks when the strings stop snapping back into place or when they break. I play about three times a week around 2 hours each session and sometimes league tennis. Before I switched to poly hybrids I was playing TNT 16 and they would last about 2-4 hours in the YT Rad Pros which is why I have the four racquets. With the longevity of the gut/poly hybrid four racquets does feel like a bit of overkill.
(4) Volkl PB 10 Mids
Babolat Tonic+ 16 @ 54 lbs/Babolat RPM Team 17 @ 52 lbs