Indeed you should. This housebuilder hasn't a clue how to build.
The whole point of timber frame is it is quick. The block can be constructed in under a week, including a covered roof.
Brickwork is then built to the outside whilst first fix and plaster boarding takes place inside.
The Covid excuse is waring a bit thin now. For a start, unless many of the trades on site got the virus and had to self isolate, there is no reason why works did not carry on regardless. Construction sites were never shutdown.
In any case if the builder has failed to plan once the virus restrictions were know he has planned to fail.
Whatever you do now, do not legally complete without a professional snagging inspection beforehand.
Clearly the builder is in no hurry so a few more weeks whilst snagging is done wont be a problem for them!
Point to note: Timber frame needs to have particular attention to sound insulation, especially the floors between flats.
It is also vital that all cavity fire barriers are fitted and fitted correctly and that other fire requirements have been incorporated in the build.