>Can I do the Covid Extension
MOST immigration offices want a 30 day extension of stay based on tourism acquired before a 60 day extension of stay based on unable to travel due to COVID-19.
>d where is the best place on Koh Samui?
You are in Surat Thani. There are two immigration offices, one in Surat Thani Muang, and one on Samui.
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. I do not know what services the office on Samui offer.
>lso would it be best to do it on Monday the 5th or is that too risky considering I'd want to reschedule my flights before then
You should be able to purchase the 30 day extension of stay based on tourism (or a 60 day extension of stay based on unable to travel due to COVID-19) when you have 30 days or less remaining on your "admitted to" stamp.
> is it instant?
You will get the extension of stay based on tourism the same day, and you should get an "under consideration" stamp for a 60 day extension of stay based on unable to travel due to COVID-19, requiring you to return in about one or two weeks (immigration office specific).