Hi again, Caz.
I'm not medically trained but as far as I'm aware, your husband is at risk of the disease spreading. He has biochemical recurrence, meaning some cancer cells were left behind after surgery. His PSA is rising quite quickly from 0.15 to 0.74 in 7/8 months.
I shouldn't worry that 'things have been left to late', but I would be questioning the recommendation of leaving it another 6 months for another PSA test.
With BCR any salvage radiation treatment is most effective when it can be targetted at the cancer cells. Sometimes they are can be located by PSMA PET scan.
It might be an idea to telephone this site's specialist nurses. Give them all the details and see what they say.
Please try not to worry. BCR is common and affects about a third of men after radical treatments. There are many on the forum who've experienced BCR. Im sure they'll be along to offer their advice and support.