How long does the Simba Hybrid take to expand after delivery, and when can I sleep on it?

It is usable the same evening. Simba's guidance is to leave it for a few hours to recover its 25cm depth after being rolled, and we found it had mostly expanded within three to four hours and fully by the next day. The faint smell from the foam, which is harmless off-gassing, fades within a day or two with the window open. Leave the protector off until it has fully expanded, and start the 200-night trial clock from delivery, not from the first night you sleep on it.