System time zone via RFC

Many of the likely function module candidates cannot be called remotely (GET_SYSTEM_TIMEZONE and TZON_* modules). Does anyone know of a function module that can be called remotely with the same (or similar) behavior?

I've identified '/ISDFPS/GET_TIME_UTC' as a possible workaround since I can count on the time being in UTC. However, I don't know anything about the '/ISDFPS/' prefix. Does anyone know what that is? Can I count on this function module being available everywhere (Basis 7.0 and up)?

Thanks for any help you can provide.