visa on arrival

Thank you for the answers. As we told already, we are 2 tourists from Belgium, visiting Vietnam in April and the first week of Mai (3 weeks in total). Do we need to send some passport pictures? Because some websites do require 2 pictures and some websites not so we are a little confused?
An other question, we will arrive in Vietnam very late in the evening (around 10 p.m.) is the office open all night for getting the visa on arrival? Kind regards