Ordinary Portland mix 7 days cure 14 days air dry.
I know what you mean about cracking, and like you would feel safer with 8 wks.
So are we back to 1mm =1day or is it
7days then water content becomes the only factor, and even more so when the heating is commissioned.
The heating should expell any water within 24hrs, so no matter if it were high or low content in 24hrs theres going to be no water.
Bal say 5days cure for their quick dry cement before turning heating on.
And of course the best way to measure this is the width of the cracks in the tiles that were laid too early.

screed
wait for it to cure
commission UFH
cool (2 days)
Tile
wait 28 days
slowly bring ufh to max temp by 1 degree a day

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