On the FTC you can set the min room temperature to be maintained so if you set this high enough you can treat Holiday Mode as a long set back period.
You can also set the min water temperature which I assume is to reduce the risk of freezing pipes outside.
Note that the end date is the last day you are away not the day you get back as I assumed.
You can see what my Ecodan did while in holiday mode here Emoncms - app view
I turned it on around 18:00 on 26/12/2023 with the end date set to the 31st as we got back on the morning of the 1st.
One thing to note is that our FTC6 main controller is in the hallway where there currently is no radiator and all the internal doors would have been shut so when room temperature was dropping to 16 degrees it was probably warming all the rooms with radiators quite high before the FTC would have seen the temperature rise.