A friend of mine does it, although she's on her second baby and now does it kind of part time - he's been out of nappies at home from being a few months old and they'd put him on the potty when they saw the signs of him needing to go, but he's in nappies when out and about. In saying that I haven't seen them for a while, he's the same age as Finn so may well be out of nappies totally in daytime now. She had more time to devote to her ds1 and he was out of nappies during the day by about 14 months I think, and going about three hours between wees so had good bladder control. She puts their success with ds1 down to spending a couple of months with her parents, her mum was doing cooking, cleaning, etc, so my friend had plenty of time to look out for toilet cues.
There's lots of info on various forums, and, as I've just discovered, on YouTube, including a 5-day old using a potty

Ok, a 5-day old being held over a potty, but it's still pretty impressive!
Good luck