If your needs are nothing out of the ordinary then I cannot stress enough that you will be better off having a needs assessment asap.
September is the busiest period for your uni, student finance (it will have to go back to them for approval) and the equipment suppliers.
You will be very lucky to get any support before Christmas, at least, if you leave it that late.
Yes it's ideal to have it done at uni as they know how that particular uni operates but it is not essential at all, trust me!
I've been told just 10 mins ago by a DDS advisor at my uni that it is a choice and depends on practicalities for the student but whatever I do, don't delay as they get busier and busier as the summer progresses and acting now should mean I have things in place at the start of my course.
Do a google search and you will see plenty of evidence saying the earlier the better.
It will help if you have some idea of the assessment types and the way your course will be run - will there be placements/exams/field trips etc as this is stuff your uni DDS dept would know or be able to find out but it's only because that obviously helps you and the assessor decide what help would be suitable for your needs on that course.
Make a local appt and if one to one support is recommended and agreed by student finance, they will provide it so get onto them to have it set up as soon as you get to uni in September.
Hopefully any equipment will be ready to go by that point if you act now.
It's obviously up to you but that's what I would do and what i've been advised to do by my uni.