OP, it depends if you and DC want to do lots of visits in person. If you do, planning a bit of a schedule and thinking about travel sets might involve some adult input or at least co-ordinating if you and teen’s diaries.
Unis are interested in the academics above all else. The predicted grades (determined through yr12 work and end if yr exams) are the most imposrtsnt thing and many unis won’t look at anything else. If you have zero idea of if your DC is a student who will be predicted Astars or As or Bs or Cs or Ds it is hard to plan Open Day visits as you need to be looking at those that are realistic for your child. Competitive courses might look at the personal statement too. It is changing next year into answers on several areas instead of Freeform writing, but essentially will be looking for the same things - why is your DC interested in the subject and what have they done to demo state this. Super-curriculars are activities they have engaged with related to the subject they want to study - reading outside of the A Level, podcast, visits, anything else and the thoughts they have had arising from them. These are always more important than extra curriculars. And anyone in yr 12 who is planning to apply for competitive courses needs to start in these now as time slips away quickly and before long it’s May/June with the start of work on the personal statement and it’s difficult then if you’ve not actually done anything beyond the curriculum. Brief mention of the extra curriculars to show skills developed is useful, but briefer than you’d imagine,
Time scales can vary a bit depending on school/college and aspirations. Oxbridge and Medical need applications in by mid-Oct (all via UCAS) so students need to have drafted their personal statement before the return to school/college in Sept and have done their uni visits and pinned down at least most of their choices by then. Some schools also encourage all students to complete UCAS applications by Oct half term, so they can then just focus on their A Levels, as UCAS can be time consuming. Other places won’t be looking at any applications of non-medics/Oxbridge before half term, but looking to get their applications in by Christmas or the end of Jan UCAS equal consideration deadline. With this kind of timetable, more autumn visits are possible.
It’s also worth knowing there are Uni Offer Holder Days for yr13s who hold offers in the spring term of yr13. Many students won’t do Open Days for all the places they out on UCAS in yr12. Instead, they might do one or two and then do an Offer Holder Day for another one in yr13 if they get an offer. MN might give the impression that all families spend 6-8 weekends trailing the country in the spring if yr12 doing Open Days and whilst some do, lots don’t and find it’s all crept up on them and they’ve missed a lot of Open Days, or simply aren’t that invested in it all anyway.
In my view, parental support and input is pretty important and gives students a real advantage. There are always total self-starters who have zero parental interest but who research everything online, get themselves to Open Days and attend a range of super-curriculars that they’ve tracked down themselves, but those are not the norm, whatever some on MN will say all teens should be like. Those whose parents have got their finger in the jokes and grasped the timescales and done a bit of research online and gently helped their DC understand the timescales and to start thinking about courses and places, do them a favour. In the end the kids have to decide what their course will be and where they like, but I do think parents can help them have fuller info and engage with the process so they have the best chance of finding out what’s available and chance of getting the best of what’s suitable for them.