Intermittent hormone therapy has probably been used much more in the UK than the US, although it's also probably not used as much here as it could be. Some research here showed it made almost no difference to the length of time it takes to become castrate resistant. Obviously, it's only suitable where the HT brings PSA down to undetectable, and where PSA is relatively slow to rise during the holiday period. For those men, they typically spend more time off HT than on it.
A complication now might be that some of these men will be on an additional novel hormone therapy medication too (Abiraterone, Enzalutamide, etc), and under the UK drug funding rules, you can't restart those after you've stopped them.
Intermittent hormone therapy is not used when you are on time-limited hormone therapy as part of radiotherapy treatment with curative intent. It's normally only used for patients who have relapsed and/or have a low metastatic tumour burden. In the UK, we have had the option to treat very small numbers of mets with SABR radiotherapy in circumstances that used to be considered incurable, although not enough centres actually offer this.
The idea of using the HT holidays to scan for mets is a good one. The rationing of PSMA PET scans in the UK may be a limiting factor, particularly at treatment centres which don't have their own PSMA PET scanners.