Well the lack of a general waste and of course no fall either outside the shower i would be worried.
The water will stand and eventually over time make its way thru the grout.
tubbed addy is safe up to a 10 mm trowel, but leaves u without the option to pack out if required
also if used in the shower recess it needs to be a D2 formulation otherwise the water will dissolve it lmao
Trev
With large format tiles and with 4 day old plaster skim I would have thought it would struggle to set in the middle. Not ideal............