Extra time for GCSE

[MarmiteAndPotatoes]

DS is on the SEN register for his anxiety (he has a ASD but it's the anxiety that he struggles with)
In primary he got extra time for for his SATs and I was told he would probably need time for his GCSEs. He's very bright but has a tendency to panic about things.
He's been kept on the SEN register to make sure he copes with his GCSEs but I was wondering when schools tell you if/when they are planning on applying for extra time? He's currently in Y10

The testing only 'lasts' 2 or 3 years. So they often don't like to test too early. One of my DDs was retested end y9 which for you would have been in lockdown so they might be behind. I'd drop the SENCO a line to ask, as they'll need to implement it for in class tests and exams to show benefit.
(It may be that being bright he gets no benefit as even with panicking he'll finish in time anyway.)

My DC had a top up assessment early in the autumn term of their GCSE year.

Perhaps you need to ask the school when they do this (there are rules about how long exam boards consider a report to be in date). If you know now, you can put it in the diary and check if nothing seem to be happening then (when there is still time to get the right stuff done)

He very rarely finishes all the questions in tests, so he normally gets all the ones he's answers right but then his score is lower as he only answers most of them.
I will have a chat with the school I just didn't want to appear pushy

Sounds as if he could benefit from extra time then OP.
There are tests needed for extra time and the requirements for this are very likely to have changed since Y6 so there are no guarantees.

I've been told it's harder to get extra time in GCSEs than in SATs. It would really help him so fingers crossed it can happen. Part of me wonders if that's why he has been kept on the SEN register as he doesn't have any actual interventions or anything like that.

If he has a diagnosed medical condition e.g. ASD then that's why he will be on the register.
It is harder than it used to be to obtain extra time in exams. I have worked with students with Access arrangements and there are fewer with extra time than there used to be.
What I would perhaps ask for is that the school can trial extra time in tests e.g. have the normal time using one colour pen and then extra time in a different colour to see the difference it makes to his performance.
With ASD and anxiety he may also qualify for using a lap-top in exams (this needs to be tried well in advance of the exams) and supervised rest breaks as needed. He would also probably have his exams in a smaller room rather than a large exam hall.
Hope that's helpful.