I would strongly advise that your student wears a watch into the exam. They may not be able to see the clock from where they are sitting and their invigilator might not give the time indications that they are supposed to. DG
I understood that with the new exam the instructions and timings were given by a CD rather than the invigilator. We are probably going to be watch-free. If the sections are short (say less than 10 mins) I think that a watch may be an added distraction for my boy. At home these last few weeks we've been doing short sections with a reminder when time is half way through and with 1 minute to go. He's built up his speed now and works as fast as he can. Now it's all about remaining calm, for us a watch would be an added stress.