At this point of time, we wouldn't know if the audit is one day or 2 day for the factories.
Looking at the location of the factory. They are both very far apart. Looks like taking 2 hours by car ride.
On my end, it has been alerted the Japan QC for contacting the factory about the availability date + asking if they are the member of the IAF - that will determine the auditing process time of 1 day or 2 day for the audit.
Also, it may be a concern on language. Not sure if the factory in Vietnam have anyone that can do the translation from Vietnamese to English for you to translate to Thai for the TISI officer.
Let's see what the Japan QC reply.