Remember any adjustments have to be 'usual classroom practice' so don't leave it too late.
In my experience it is much harder to get any additional time for 11+ than for GCSE, A level or university exams.
My experience of extra time in the 11+ for Kent is that it is only awarded for the 'story' which is only looked at if there is a HT review - 10% extra time was given for this and nothing for the two tests despite an Ed Psych report. Another parent of a dyslexic child said to me that Kent don't give extra time to dyslexics in their tests. I don't know how true this is, but it is certainly applies in all the cases I am aware of. I would love it if someone on here could contradict this and say they were given extra time in the tests.
Do be aware that for Kent any special need requirements have to be requested by your school and not by you as the parent. Also, you may not get a response to this request until you go back to school in September. In some other areas e.g. Bexley the school or the parent can apply and responses were received before the summer holidays.
My advice when doing practice tests before the 11+ is to try to stick to the timings given as you may only find out a week before the tests that you won't be getting extra time.
Forgot to say - Have also PM'ed you