@Graham ********
I just done it a few days ago. It takes between 10-30min. You apply, pay, they take your photo, you give documents, you sit and wait. At the desk that says are-entry permit prior immigration before heading to your gate. It’s easy. Important to know that They take only cash. Its important to do so she don’t loses her extension when she re enters the country.
If you want to be ready and make sure, do it at your immigration office a week before departure.