any other person permitted by you, as (A)RO, to attend
You need to be satisfied that it will not impede the verification or efficient counting of votes and that you have either consulted the election agents or thought it impracticable to do so.2
You should take all necessary steps to ensure that anyone attending does not interfere with or compromise the secrecy of the vote. You are legally required to make such arrangements as you think fit to ensure that all attendees are provided with a copy of the relevant secrecy requirements.3
You have a legal duty to give counting agents reasonable facilities for overseeing the verification and counting of the votes. You should ensure that anyone who is entitled to attend has an unrestricted view of the proceedings, without being able to interfere with the work of your staff.4
There is no requirement for those attending to arrive by a certain time. You should have a process in place to ensure that, those entitled to attend can be admitted whenever they arrive. This process should also allow any attendee who wishes to leave and return later to do so.