Here's when that time translates to around the world:
• 11 am Pacific, July 6
• 2 pm Eastern, July 6
• 7 pm BST, July 6
• 8 pm CEST, July 6,
• 4 am AEST, July 7
Never played a Diablo 3 season, but based on what I heard those were fairly well received at the end. They've said they want Diablo 4 seasons to be an even bigger deal.
Not sure what to expect, but more to do would be cool. Path of Exile does a great job adding to the endgame with its leagues so something like that would be awesome.