I think it's one of those 'it depends' things. If there's no real fighting within the first day then you're off to a promising start but I would say it generally takes a couple of weeks for them to truly settle with each other though low level dominance displays will continue indefinitely, particularly if there's something worth arguing over (even if you provide two of everything). My boars have been together happily for nearly a year and a half and Blondie still gets somewhat, erm, "rambunctious", shall we say, and tries to mount Hermes and they'll have a little nose off and rumblestrut at each other but then they popcorn everywhere. They also like to argue over the stool which is their favourite hidey, again, usually it's Blondie being the antagonistic one.
There is also the factor of age, between 4-14months or thereabouts is the major hormonal phase during which you can expect more displays of dominance behaviour and it's the most likely period for fallouts to occur even in previously stable bonds.
But as I said I think it depends on the individuals, I'd imagine some pair up quickly and some take a little longer to settle their differences as reflected in the different bonds they have. I've read and seen pics on here of boars cuddled up together and ones that will groom each other. My two will sit next to each other in the hidey but don't tend to cuddle up and I've only seen them groom each other once (quite recently) however if I take Hermes out the cage without Blondie then Blondie stands and the bars wheeking for him and they seek each other out when they're frightened.
