If I book the e-Visa On Arrival extension, can I also extend it immediately after arrival?

No, this is not possible.

The extension can only be started earliest 14 days before the current e-Visa on Arrival expires.

You are welcome to place your order at any time on our website, but we can only submit your extension to Immigration once the 14-day window has opened. As soon as it becomes possible, we will start the extension automatically.