Yeah, less than a month before the event. That being said, that was when they announced the venue too. They've said that they want to organise things sooner to ensure people can also organise themselves better too. So it wouldnt surprise me if it was done much earlier, clearly they're planning thing much further ahead now.
July would be a decent timeframe, 3mo beforehand. Its a vicious circle though, dont want to book in advance incase you dont get a ticket, dont need a ticket if its too expensive to arrange everything.
I've no idea how quickly tickets sold, they sold 200 $2.5k Jav's in minutes, not sure how long the 300 CitCon tickets took to sell. PAX Aus took weeks, but then the population density is nothing compared to the UK, it'll be accessible to anyone in England, Scotland (most of) & Wales within a few hours drive, 4-5 in more remote areas i suppose, but a good 40m ppl im sure.
For purely selfish reasons, it'd be better for me if they were sold the day before and 90% of ppl didnt bother (cos im local, less competition), but really it needs to be at least 2mo beforehand really.
CitCon will almost certainly be the first time we see SQ42, whether its the just opening cinematics or a full on release, its expected around then and they wouldnt do it earlier, they'd want to do it here in Manchester with all the team there IMO, but i suspect it wont be a 'release party', just the first time we'll see something of substance. Looking forward to it.