With modern low-VOC paints, many people comfortably sleep in a freshly painted room after a full day of good ventilation – roughly 24 hours. Keep windows open as much as possible, use fans to keep air moving, and leave doors ajar so fumes don’t concentrate.
If the paint has a strong smell or you used oil-based products, it’s wiser to wait longer – perhaps 48 hours or more – especially for children, elderly people or anyone with asthma or sensitivities. Trust your nose and body; if the room still smells intense or gives you a headache when you sit inside for a while, give it more time.
You can speed things up by removing any paint trays, roller covers and used cloths from the room once you’re done, as they continue releasing odour.
The goal isn’t to hit an exact hour count, but to make sure the space feels fresh enough that you’re not breathing heavy fumes all night. When in doubt, sleep in another room for one more night.