I would definitely mention it. It’s bothering you and your elderly neighbours. Chances are...they haven’t thought about the effect it’s having, and it’s almost not fair not to give them a chance to sort it out.
However, if you get no joy, I would just document everything Then if you do have to go down the complaints route, you’ll have evidence. Hopefully won’t come to that. It’s so easy these days with smart phones if you have one.
You say they’re quiet at night, which is the real blessing, although it shouldn’t have to be. I always feel you shouldn’t have to ask twice, they’re adults. They’ll either stop immediately you tell them...or not, or they’ll give you a good reason, and a possible stop date.
Whilst documenting, are there changes you could make? Such as moving your sitting area in the garden to outside your house?
At least it’s winter now, so presumably no sitting outside. Hopefully, any work he’s doing will be finished by next Spring.
Good luck.