Re: underfloor heating and thermostat and using adjustable timer / temperature etc.
My house is Passive House, and as I understand it definitely would be best to run UFH 24/7 and just adjust the flow temperature to a few degrees above ambient, but I don't do that. The response time of any heat input (given huge heatsink in the floor) is so slow that it is very difficult to adjust anything in a fashion that is "useful". What I've found works for me is to set overnight to, say, 1C below target (if temperature actually falls that low then it would come on), set Day to target temperature - if the sun comes out no heating will be will be needed, if not, and temperature actually falls to that level then heating is needed; and set the "Getting up" and "Evening" to 1C over target. Thus they will, invariably come on (although Evening won't if day was sunny as room will already be 1C, maybe 2C, high). That charges the floor (and the rest of the thermal mass in the room).
My plan has always been that if we get a spell of really cold weather I will either increase flow temperature, or the duration of the "overheat" periods, but the last time we had a solid week of artic winter temperatures I never got around to it (typical, for me!) and actually the house daily minimums only fell 0.5C lower than regular winter nights.
If we go away for the weekend in mid-winter and turn everything off the house will lose 0.5C ~ 1C - haven't used any heating yet this Autumn (we have had some frosty nights ... albeit mild recently), and I don't normally expect to until at least mid November. Can't understand why Building Regs don't require Passive Haus for new builds - less than 7% on the build cost, and virtually no heating costs for the lifetime of the building, and can choose to have no boiler at all (use an electric fire on the few cold days each winter) and then have no maintenance / replacement either ... unfortunately retro-fit passive House / EnerPHit is eye wateringly expensive.
So maybe setting a conventional thermostat to over-heat for a few hours in good time before getting up, and before the evening period, and "normal" for the day (if at home) and a bit low overnight would work on UFH systems that have huge-lag / slow response?
But undoubtedly the main benefit I have is the insulation level for Passive Haus. My advice for anyone contemplating a new-build is to go Passive.