Depends on what the goal is.

You can sleep in it whenever without hurting the mattress, it just won’t be as comfortable.

However, if you’re worried about offgassing, there’s differing opinions based on the exact materials, but the worst is going to be the first 24 hours or so. If you’ve got good enough ventilation, even that’s not a hard stop limit, but it’s not going to smell very pleasant for most people.

Smell wise, at least a day, with two being where most people don’t mind whatever chemical smell is left.

But it’ll be putting out lesser amounts up to about the 5 day mark where any materials in common use will be emitting as little as they ever will on a practical level.

I tend to favor the third day myself. The smell is tolerable to me by then, though I’ll likely be a little clogged up for the first night or two after that anyway.

So, it’s really up to you at this point, it’s as ready as it needs to be to give acceptable support.