Is it easy to change booking if needed and change at any time? Is there limit to number of changes, etc.?

Since it is a booking, it should not matter what time you book, correct? I had been going (walk-in) in morning, but prefer late afternoon.

This for Non OA extension if that makes any difference.

Thanks.

At this time very easy to change appointments (did few days ago for this week) - after all have to use will obviously result in less open times but probably not be an issue if not wait until last day to do.  As far as I know there are no limits - you just cancel and make new.

OP, just open appointment booking as though you haven't made one yet. Early on a small drop down screen appears. Think it was in Thai. Basically it means if you proceed your existing booking will be cancelled.

Accept and proceed with new appointment.

BTW you need to take hard copy of your confirmation email to immigration.

As soon as you make a new appointment, the old one is cancelled on the system.

Now impossible as system down U