If patients are not having CT, then they do HT for 3-6 months before starting RT. (The HT before RT is called neoadjuvant HT. The HT after RT is called adjuvant HT.)
I think CT at this stage is usually 6 cycles of 3 weeks each, i.e. 4½ months, so I think your RT will be around 5½-6 months after starting HT if the CT starts a month after HT, but that timing isn't critical. For some cancers, the RT is given during CT, but I don't think that's done with prostate cancer.
Thanks for the comments. I've recently been asked to teach a class to therapeutic radiography students at University of Suffolk too, but do bare in mind I'm a patient, and not a clinician, so do check this with your oncologist.