twice. Once on 30 exemption and once on 60 day Tourist. Extended both times for 30 days. Gap in between as toured round Vietnam, Cambodia and Hong Kong.
2-3 month gap this time to tour round Indonesia and Malaysia.
Did this recently. So easy at the embassy in Phnom Penh. As Tod says allow the 3 working days as long as you have the paperwork all correct which is straight forward and easy. Don’t pay for an agent.
you’ll pop back 3 days later (between 3-4 is the only time allowed to pick up the passport with the visa) so unless you have a late flight you’ll need to stay in your hotel that night too!!