The plumbers said that screed is 'dry' if the humidity is between 20 and 30%. So today I went to the house to measure the screed humidity.

The results are:

Place Humidity (%)
Cellar
Utility 17.7
Basement 1 15.7
Basement 2 15.7
Laundry 17.4
Ground floor
Guest 17
Living 15.7
Dining 15.7
Kitchen 15.7
Shower 17.5
Storage
First floor
Child 25.2
Storage
Bathroom 19.7
Bedroom 19.6
Study 17.7
Landing 17.7

So, by all accounts, the screed seems to be dry enough.

HTH,