A set moves at the speed of its slowest sheet
Most people filing anything in Yemen are not sending a single document. They are sending a small pile, gathered from different places at different speeds. The Arabic writing takes the days it takes, but that count cannot begin until the pile is whole, so the sheet you are still waiting on is quietly setting your calendar.
Why the whole set is read at once
Reading everything together is not a preference, it is what keeps a file consistent. A name spelled one way on one sheet has to be spelled that way on all of them, and the same holds for places and for dates. Splitting the work across weeks invites two renderings of the same word, which is exactly the mismatch a reader stops on.
What is read at the far end
Yemen works in Arabic, so every sheet you file needs Arabic beside it. The certified form used on this route is the one written to be read by consulates and ministries: a Certified Arabic translator signs and dates a statement of accuracy, which then stays fixed to the pages. That statement is what makes the Arabic more than a helpful rendering.
The count, the days and the express route
The rate is £25 for each side of paper as issued, totalled across everything in the set. Standard work takes 3–5 business days from the arrival of a complete, readable scan, and the express route brings that down to 48 hours. Express shortens the writing only. It does nothing at all to the part of the wait that happens before a scan exists.
Chasing the sheet that is missing
Where the gap is a birth, marriage or death record, Stoke-on-Trent Register Office issues fresh certified copies from the Civic Centre on Glebe Street. It runs by post, so nobody has to queue, and your own certificate need never travel anywhere. Getting that request in early is worth more to your timetable than anything you decide afterwards.