My go to for home automation is Home Assistant and there is an integration for this make of HP STIEBEL ELTRON - Home Assistant - might not be the right model, but if they use a common API it might be OK.
HA has got sophisticated automation mechanism, but less good on the scheduling side. I use a HACS add-in called Schedy to schedule control of the set point temperatures on the climate integration, and then the climate integration controls the actual switching.
I do something similar with HA, AppDaemon4 & Shedy.(hass-apps). For example I control the max/min temperature of the DHW tank depending on time of day - Hotter, and higher minimum during a shower period, cooler rest of day for hot water (more time to recover so can be allowed to get colder) No heating of tank unless UFH lowers the temperature too far.
With those tools, it is very easy to do and to change.