After seeing a physiotherapist i was told that my knee pain is caused by weak glutes. is this severe and how long should i take off running?

No : Weak "glutes" are generally not a severe condition and it would be fine to progressively resume normal activities such as running, as long as your pain/strength allow for that. Having said that, weak quads would actually be much more likely to be a cause of knee pain, so i would clarify with your physiotherapist and your doctor as to your diagnosis.

Knee pain in runners: Knee pain in a runner can be due to a myriad of different things. I invariably see weak gluteus medius and hip abductor muscles in runners, especially distance runners. While it is probably not the only direct cause, it is probably contributing to your pain and needs strengthening. You should continue to follow up with pt and no run until you can do so pain free.