Server down time for game update: 6/28/17 at 9:00 AM EDT (GMT-4)

From official site forum

The Elder Scrolls: Legends servers will be unavailable at 9:00 AM EDT (GMT-4) on Wednesday, June 28 for a game update to Heroes of Skyrim (build 1.65). The estimated duration for this downtime is 6 hours.

Edit: The official site forum corrected their typo. According to /u/_Scapes_, "The game update is on Wednesday, June 28. The Heroes of Skyrim launch is announced on Thursday, June 29."