[This post is only expressing own opinions, non-related to my agency].
People who want to stay in Thailand for more than 30 days for travel, work or other purposes have to get a Non-Immigration Visa. For more than three years I was living in Thailand with a Non-Immigration Visa (ED, Student) but it was time to change to a real work permit. With the right papers from your employer it usually takes 2 weeks, sometimes a bit more. But my whole process took nearly 14 weeks and I stumbled upon a variety of upsetting hold-ups and snafus.