1. It might be tough getting in for the take-off if they're busy, and you're not known.
2. Its a long flight, and if you get a visit early in the cruise the "interaction" might peak early, leading to you having to return to your seat
3.I would, on boarding, casually ask the CC to give your liscence, or passport with a "SHORT" note to the Captain asking for a visit when he's not too busy
If they forget, ask again about 1.5 hours out, probably your best chance of being there for the landing
GOOD LUCK!!