As soon as he wants to be. If he wants a job tomorrow in Detroit it's his. If he wants to take the month and maybe go to Jamaica? He can do that too. Maybe he wants to wait until the offseason and see what comes up, while making Vegas pay his contract the whole time? That's his option as well.
Teams looking for a new coach (or in the market) would snap him up the second he is available. The question is does he want a job right this second.
Claude Julien and the Habs a few years ago is a good example. Montreal had Therrien and Habs were having an ok season (not great) - in playoff spot. As soon as Julien got fired - within the same 1-2 days Habs fired Therrien/hired Julien.
Now I think Therrien was way past his time as coach - and as a Habs fan to this day i'm still not exactly thrilled with Julien - but the point is Julien was seen as a coach who would likely be very sought after - and a team who you wouldn't have expected to be on the cusp of firing their coach, did so asap to snap him up before another team got him.
So - I agree that he could probably get a job "when he wants", as he's a good coach. But i'm more curious looking at it from teams perspectives - which teams who aren't 100% confident that they will bring their coach back for next season - are willing to take a gamble right now before Gallant gets snapped up? I'd argue Gallant today is probably an even better candidate than Julien was when hired.
I know you're a Tampa fan. If Tampa hadn't literally just won 10 games in a row - they would be a prime example. In playoff spot, doing ~ok (not great) - but status quo, or take a gamble on a great coach before he's snapped up? I'm sure there are other teams like that who might be tempted.