Don't get the idea that hormone treatment is somehow hanging around or waiting to start bashing the cancer. The bashing began as soon as that Prostap hit his body.
There are two types of hormone; one starves the cancer by stopping production of testosterone (Prostap is one of these) and the other disguises testosterone to trick the cancer into thinking there isn't any. No testosterone = starved cancer cells = disrupted growth and shrinking tumour.
Your dad may be on one hormone or both, or both for the first month and then just one. Hopefully, that hormone will control the cancer for many years - we have members that are still here 10 and 14 years later because the HT is still working. Sadly for some men the HT only works for a few months - for some it doesn't work at all but they are very rare. Your dad will be monitored so that any sign the HT is failing is picked up quickly.
When HT fails (this is called being hormone refractory), there are a number of newer treatments like Radium223, abiraterone and enzalutimide which can hold the cancer for longer. Chemo does not kill prostate cancer and until recently, was only used when a man was at the end of life stage to make him more confortable. Some recent research has shown though that chemo given earlier makes HT work better so some hospitals would now offer this to your dad but it isn't available everywhere or he may not be thought to be strong enough for chemo at the moment.