Leesa recommends unboxing the Original Mattress within 30 days of purchase and the Sapira Hybrid within 60 days.

The manufacturer doesn’t mention anything about its other mattresses, but it’s best to unbox your product as soon as possible.
The longer you leave it in its box, the higher the risk of damage. Plus, your mattress may take longer to reach its full size if you leave it rolled up for weeks.