Practical completion is the stage where the property is deemed to be safe for habitation i.e fully functioning electrics, heating and plumbing, lights working, kitchen in, tiles fitted, appliances fitted and working, taps/shower installed, etc etc... but at this stage there many still be cosmetic work to do i.e final painting, touch up's, cleaning etc etc...
yes by all means you should be able to inspect the property before legal completion (this would be ur demo visit 5-7day before legal completion) where you can check things like your kitchen, bathroom and flooring choices are all correct, the correct spec has been followed, everything works, water, drainage, heating, electrics etc etc. However at this stage there may still be cosmetic work to be complete (depends how quickly the builders want to handover). But i agree with you, it is a pain in the @rse having to take time off and sit around and wait for builders, but unless you give them unsuppervised access... it will have to be done.
But the point im making is if your getting a snagging inspector (which i asume your paying for) to inspect before handover you will still have to inspect again after completion (whether on your own or with a professional) Ie. If the builders still have a final coat of paint to do they might leave marks on the switchs/tiles... and the property will be cleaned just before handover the cleaners might scratch worktops, mark taps or carpets etc etc...
If it is a legal obligation for builders to work to your schedule I dont know anything about it cuz it certainly doesnt happen... so i couldnt really comment on this.
Clare