I am not doubting anything that has been said here but I remember going to Laksi in 2009 and there was a big notice saying the express service for authenticating affirmation translations had stopped. They still did mine the same day though. I have an appointment booked at the British Embassy for 8am on 3 January for my Affirmation notarising and will be heading straight to the translation service and on to Laksi as soon as possible after that. I will try to find out what options are available and post details.
I don't like using agents but if there is a few days wait at Laksi, an agent may work out cheaper than paying for a Bangkok hotel and sitting around waiting for days as the agent should be able to post the authenticated translation to me (at my home in Khao Yai).
However, there appears to have been a change in the way that the embassy does things with the affirmation. It used to be that you could hand the affirmation and your documents in in the morning and collect them after 1pm. I didn't see any mention of that when booking my appointment, can anyone confirm that they now do it whilst you wait or otherwise?
Also, many of us here used to use the services of a gentleman called Mr Preecha. As long as you had your affirmation done, he would handle everything, including the MFA. He has retired but last time I looked, his company, Original Translation Center, was still operating - run by relatives I think. I'll try to find out if they can still assist with all or part of the process.