There was an announcement on the official forums regarding an upcoming change to the Guild Trader reset times on August 11th, 2020.
Here is a mobile-friendly summary.
What?
Zenimax Online Studios will be adjusting the date and time that Guild Traders make their weekly swap to coincide with some backend work going into Update 27.
When?
Beginning on August 11th to coincide with some backend work going into Update 27.
Why?
These new times will ensure Zenimax Online Studios can fully monitor and react to any issues that may arise when the swap takes place.
How?
The previous week will be extended two extra days to end at the new reset time.
European (EU) megaserver: Tuesdays – 14:00 UTC, 10am EDT / 9am EST
- 13:55 Tuesday UTC: All bidding and renting from the previous week will stop
- 14:00 Tuesday UTC : Tabard of the selected vendor flips to new owners
- 14:05 Tuesday UTC : All bidding and renting is opened up again for the following week
North American (NA) megaserver: Tuesdays – 19:00 UTC, 3pm EDT / 2pm EST
- 2:55 Tuesday EDT: All bidding and renting from the previous week will stop
- 3:00 Tuesday EDT: Tabard of the selected vendor flips to new owners
- 3:05 Tuesday EDT: All bidding and renting is opened up again for the following week
NOTE:
Zenimax Online Studios will also be testing this time shift on the PTS, with August 4th being the first time it changes on that realm. If you are a GM of a guild on PC EU and would like to help us test, please post here and let us know.
SOURCE:
https://forums.elderscrollsonline.com/en/discussion/540142/updates-to-guild-trader-swap-times