It really depends on the nature of the surgery. Total hip replacement, bipolar hemiarthroplasty or DHS?? If the patient previously had, say, intra-articular steriod injections earlier on in the pathway, then they have had their first definitive treatment which has to happen within 18 weeks of the Consultant receiving the original referral.
If surgery is not the first line of treatment for the same condition, there's really no enforceable time limit.
It depends on the popularity of your surgeon, where you live, and other factors. I used to work for two Orthopaedic Surgeons. One had a waiting list of 5 weeks, the other 33 weeks.
If you keep ringing the Secretary and make a nuisance of yourself as politely as you can, your waiting time MIGHT be expedited.