Most universities encourage people to arrive the weekend of freshers week, Friday-Sunday which means you’ll be at uni for all the inductions, troubleshoot any admin, register in person (which is needed to get student finance maintenance loans).
In practice you can normally miss a few days of this if you can’t make it although I wouldn’t recommend this, as it’s a great way to make friends & get a feel for the place (and freshers is a lot of fun).
You can arrive whenever your tenancy agreement starts, halls typically open the Friday before freshers week (if you are an international student sometimes they will make arrangements to help you move in earlier).