A deleted site is not destroyed immediately. Sites → Deleted sites.
What happens when you delete
The site stops serving and stops counting against your plan straight away. Its files, database and backups are kept for the retention window shown on that screen, and only then destroyed.
Restoring
Open Deleted sites, find it and restore. It comes back with its files, its database and its backup history. Two things do not come back on their own:
After the window
Once the retention window passes, the data is gone and we cannot get it back — not from a backup, because the backups go with it. That is the whole point of the window, and it is why the screen shows a date rather than "soon".
⭐ If you are not sure whether you still need a site, delete it rather than keeping it. The bin gives you the window to change your mind, and a deleted site stops being billed on the day you delete it.