Keep a round under a minute
Thirty to sixty seconds is the range. Longer and the queue stalls and disperses. Shorter and nobody has time to commit or to be watched doing it.

We have been watching what works on a show floor for twenty-odd years, and this is roughly what we would tell you over the phone.
The single most useful thing to understand about stand footfall is that people join queues, and not usually because they want the thing at the end of it. A group of people stood watching something is about the clearest signal you get on a show floor that it is worth a look. One person having a go is just one person having a go, whereas five people waiting their turn is something you walk over for.
That has a practical consequence, which is that the game is not really the attraction so much as the thing that produces one. Once you look at it that way, most of the decisions further down get easier.
They are roughly in order of how much difference they make.
Thirty to sixty seconds is the range. Longer and the queue stalls and disperses. Shorter and nobody has time to commit or to be watched doing it.
A game against the back of the stand makes people cross a threshold to reach it. On the aisle edge, they can play without ever deciding to walk onto your stand, which is a much smaller decision.
A visible leaderboard turns single plays into a competition that runs all day and gives people a reason to come back. It is also the cheapest thing we hire.
A game with nobody next to it gets walked past. One person whose job is to say "do you want a go" roughly doubles what the same kit does on the same stand.
The prize does not have to be worth much, it just has to be worth entering for. A daily winner beats a big draw nobody expects to win.
Plan where the line forms before the show, or it will form across your neighbour's frontage and you will spend day one apologising.
In a client's own words
A client running a branded grabber at an evening event told us afterwards:
Such a great idea for our event. The queues for the grabber never went down all night. The branding done for us looked great and service fab from start to finish.
A grabber is a good illustration of the principle, because the play is about fifteen seconds, the outcome is visible from a distance, and the win rate is something you set rather than something that happens to you. All three of those feed the queue rather than the individual player.

Worth being clear-eyed here, because the two are not the same thing and a game can be very good at one and useless at the other.
Anything with a big physical spectacle brings people over and holds them, but it tends to attract everybody in the hall rather than your buyers, and the person watching is not the person you want. Free food does the same only more so. Both are fine if brand awareness is the brief. If you are counting qualified conversations, a quieter game with a data step in it will beat them, and our guide to lead capture covers how that step works.
The first is putting the game where you would like it rather than where the traffic is. Aisle frontage is worth more than a tidy stand layout, and if the choice is between the game sitting awkwardly and the game not being seen at all, we would take awkward every time.
The second is leaving your best person on the game. The game does not need your best person, it needs somebody friendly who does not mind repeating themselves. Your best person wants to be free for the moment the game hands them somebody worth talking to.
Everything above assumes the kit fits, which is not always a given. The power and space guide has real footprints, and shell scheme versus space only goes through what each stand type will take.