ᐅ Screed on Concrete – When Is It Possible?

Hello everyone!

I am currently renovating an old house—room by room. In the study, there was a wooden floor on joists, but now everything has been stripped down to the shell.
As of now, in the current room: about 20 cm (8 inches) below the target finished floor level, there was a rather patchy concrete screed. On top of this, I laid a construction vapor barrier (with edges extending up the walls). I poured about 25 batches of concrete into this 11 square meter (118 square feet) area and leveled it reasonably well. So far, so good. Now my questions:

1. Some areas have set firmly. Other spots, even after 5 days, are still somewhat "clayey," so I can scratch a groove with my fingernail. What does this mean? Is this a problem?

2. When can the next floor layers (vapor barrier, insulation boards, screed) be installed? The screed installer said today it doesn’t matter if the concrete is still fresh. He wants to install the vapor barrier, insulation, and screed already in 2 days (i.e., 6 days after pouring the concrete). Is this possible, or is that too early?

Thanks in advance for your answers!

For clarification: By concrete carpet, I mean a patchwork of concrete that was apparently poured at different times. 25 batches means that I mixed 25 batches of concrete myself using a mixer and transported them in a wheelbarrow.