Immigration offices in Thailand are notorious for their long queues, especially for tourist visas, education visas, and business visas. It can easily take you the whole day for a simple tourist visa extension. This is one of the main reasons many people decide to use a visa agency: to simply reduce the queuing time.
The best time to go to the immigration office is early in morning. Although it opens at 8:30 AM, you should be there around one hour before it opens. And you should still see a busy queue there already. Make sure you have the visa form completely filled out and documents ready.
Failure to do this could cause you at least an extra hour at the immigration office. The form could be found right at the immigration doors.
If you cannot make it for the early morning, going there in the afternoon around 1PM to 2PM is an option. Don’t go after 4 PM at all costs since the immigration office stops accepting new queue numbers at this time.
The worst time to go to the immigration office is around 10AM to 11AM. There will be a lot of people there already. And the immigration officers have a lunch break for an hour at 12PM. During that time, no one is allowed to wait inside the office. It means you will waste an hour just standing around.
Monday usually has the least number of people.
For other visa types such as marriage, retirement, media, and so on, queues are not that long compared to three aforementioned visa types. You can go to immigration anytime you want. But going there earlier is still your best option.