See I think that is very firm dependent because in both VS I have done there were quite a few people with additional time who got both (even in very small VS cohort).
I think in one VS of 13, 4 had additional time and one of 9, 2 of us had ( but we were only 3 at the AC)
I think it really depends on the firm. Some are definitely really bad even at giving additional time for tests and stuff but ultimately I do have some conditions that will never go away and would not want to work for a firm that would discriminate based a on few more minutes. Especially because yes a deadline is a deadline but you can always work a bit later to make sure you meet than deadline if needed. So I get it is a pressured environment but you can also adapt how you work to make sure you meet their expectations.
I have adapted where I applied because I can't see myself working at a firm where very lates finishes are common, partially because of this. Many lawyers have adhd or dyslexia for instance and are very successful and I am sure many firms are aware if that.
Ultimately I think you have to choose whether you can make it without adjustements and which ones are reasonable for you. I used to never pass the test stage because of my lack of time. Since I have disclosed it, I have passed a lot more tests and went to next stages regularly.