Plastering above half wall tiles, before or after?

Hello, and happy Easter! I am about to have my bathroom re-done, and we will be having 3 walls half and half, with the bottom being tiled, and the top plastered. I have a tiler coming next week, and I will be removing the old tiles, repairing (or plaster boarding) the walls depending on the condition, and plastering the top areas that wont have any tiles myself.
Should I do this before or after the bottom half has been tiled?
I have reasons for and against both. If I did it before, I would need to workout where the top of the tiles finish as to not skim the bottoms under the tiles (impossible?), but would be no chance of making any mess. If I did it after it would slightly build out the walls closer to the face of the tiles (covering the adhesive gap and some of the thickness of the tiles) but might be difficult to do neatly. I don't have the time to skim all of the walls so they can dry properly before tiling over it, so that is not an option.
Thanks in advance for your input!

 

Thanks Steve! Just ripped off a few tiles on each wall, appears it has been plastered before it was tiled last, so should be ok to tile straight onto. Would the area of feathered plaster not take too long to dry out to be tiled on next week? And would I be better off using a quick set tile adhesive to patch the bottoms if need be as opposed to the plaster, again because of the drying time? Or am I overestimating the time? Its a good job I've still got a week to get this sorted, but will get on it sooner rather than later. Thanks again

 

I suppose the patching depends on the depths so will encounter that if and when. I will just rip it all out and off tomorrow then I still have plenty of time, even if I wont have a bathroom for at least 2 weeks. (Temporary outside toilet to be bodged, and showering elsewhere will be in order!) Cheers