The true is that nobody can say nothing sure now. During the weekend they move their office, monday keep closed to check all machines and informatic system is working. If all is ok, they promptly communicate to re-open on tuesday, at the latest on wednesday, I think.
The most trustable info is that they should finish moving all furniture and machines on Monday 2nd evening. Only then they can check if informatic system is ok, then could open on 3rd or at the latest on 4th.
In case of persisting problems with informatic system, office closing time could be longer...
You will arrive to Thailand with a 30 day visa exempt stamp. Once in Koh Samui you can extend it by 30 more days just going to Immigration Office.
Till 60 days you don't need any border run nor visarun, so no need to pay any agency service. I attach a photo with what you need to buy an extension at Samui Immigration (open Monday-Friday 8.30-12.00 / 13.00-16.30).