For changing from ed visa to non b, got cancellation letter from university in which last date is 20 December.
So go to immigration for cancellation in first week of December and then go to lao visa run first week and come back before 20 December. It is ok to enter with non b.
I am wandering ed visa cancellation is effective on date of going to immigration or 20 December.
TLDR : Answer Summary
User is inquiring about the effective date of their ED visa cancellation after visiting immigration, considering they have a cancellation letter from their university dated December 20. They plan to do a visa run in Lao and want to know if the cancellation is effective immediately upon going to immigration or on the letter's date.