This depends on your method of construction, and whether it’s the first day of the heating season, or you are a few days/weeks/months into it.
The more thermal mass you have to heat up, the greater the thermal inertia, and therefore the more energy (and time) required to heat the rooms up.
So an insulated screed that is 60mm thick can take ~15-30mins to heat up, and an insulated on-ground slab (125mm thick) can take 30-60mins to heat up.
The first few days of the heating season it takes longer to heat the rooms up.
This is because the floor is completely cold, and so are all the walls, ceiling, furniture, etc. (the floor heating radiates heat to these objects, therefore warming them up and making them into heat emitters too).
