I had a neighbor once who seemed to be rehabbing their unit nonstop from dawn to dusk for six months straight. I moved because it was untenable...it becomes a bit like psychological warfare and you can't even hear yourself think. Understand that, while you have a right to work on your unit...if it's nonstop, it is a nuisance to people around you. Especially if they study/work from home. Drilling, pounding...day in and day out and at every available hour is an awful way to have to live for a long period of time, it's loud...very loud. That's more than just a door closing, or being able to hear footsteps, a bit of residual music the neighbors have on while they're tidying up their place. Headphones and earplugs don't really work with that sort of construction sound, sadly. So I feel like he's not asking for complete silence, probably just wants the incessant droning of construction noise to take a hike.
I don't know how long you expect to be updating the unit, but a little understanding goes a long way. Perhaps he's a bit sensitive, but depends on just how long it's all been going on and how long you intend to be renovating. I know what it's like to live next to someone doing those same projects that never seem to end. Is there a way to get an estimate on when your rehabs will be finished and simply speak to the young man and tell him you're sorry it's been a bother but you'll be done by a finite date and you wanted to get everything done at once so it wasn't stretched out even longer?
As far as lawyers, I don't know any that deal in neighborhood affairs but is there a way the administrator could act on your behalf? It seems like if the admin isn't too concerned, you can simply state your case in response to the Carta with an estimate of an end to the construction and that could ease any more problems?