I would leave them until all the chases have been cut, boxes fitted and the first fix completed then fill them with bond, leaving it 2 or 3 mill below surface. I generally make the bond slightly to watery, because it can take a while to fill a lot of chases. I would then return to skim over the bond when I am second fixing.
The trick is to blend the skim in, so its plastered over each side of the chase by about 4 or 5 inches, then go away and plaster over another 1 or 2 before returning to the first, by now it will probably be drying, so use a sponge to wet your trowel before going over it again but you will need to keep your trowel wet and you will get a better finish if you keep the water clean.
Plastering is really not difficult, just takes a bit of practice and patience.
Ian