In Phnom Penh it's 3 working days and it's very easy to fill out the form and hand in and pick up yourself. The times for handing in and picking up are different. 9-11am for handing in I think. 40$ for 2 month tourist visa.
I went to the Phitsanulok office about a year ago asking could I extend for 6 days, I had no ticket to leave. They gave me the extension with no questions.
I've obtained SETV in Phnom Penh several times in the past with no issues. However they can be pedantic with the required documentation especially bank statements need to be certified ("stamped").