Yu-Gi-Oh! Master Duel will go under maintenance for a few hours on the 27th of January, between 1 AM and 7 PM GMT (this translates to 5-11 PM on the 26th PST, 7 PM on the 26th - 1 AM on the 27th EST, 2-8 AM CET). 

During the maintenance, the game will be unavailable to play. The Secret Pack countdown will continue during this time. Finally, Rooms and Match Histories will be reset in order to improve server connection.

Quote From Yu-Gi-Oh! Card Games (KONAMI Europe)

Attention Master Duelists!

#YuGiOhMasterDuel will be undergoing maintenance on 27th of January between 01:00-07:00 GMT. The game will be unavailable during this period - we apologise for any inconvenience.

Please note, maintenance may conclude earlier or later at short notice.