Screed residual moisture and vinyl flooring

Hello dear all,

I have two questions and hope that I am in the right place here.
We received our screed on 5.5.17. Everywhere anhydrite, except in the utility room, guest bathroom, and bathroom, where it is normal cement screed.
The heating-up program of the underfloor heating has also been finished for about a week now.
Since we are laying the floor completely ourselves, both vinyl and tiles, we do not have a floor layer who performs the CM measurement.
Now I am wondering, after such a ‘long’ drying time with really good weather etc. (the last weeks were wonderful), can we assume that the screed is dry enough? I also just read something here in the forum about the hand test and will still try that.
The relative humidity upstairs is currently mostly around 50% and downstairs 45%; during the weeks when it was so hot, we averaged about 38% humidity, which, as mentioned, was due to the extremely warm and, apparently, dry weather here (we already had 38% two weeks after the screed was laid).
So much for question no. 1, now to the second question.
In the order confirmation for the vinyl flooring, a vapor barrier foil is listed, do you absolutely need this and if yes, what for? The floor slab is insulated, etc.

Many thanks in advance.

Regards
Anna-Lena

Small edit: The vinyl floor is to be installed next week. The drying time is therefore 5 weeks until then. Tiling work on the cement screed will probably begin at the earliest in 3 weeks.

I wouldn't dare! If I were you, I would borrow a measuring device to be certain.