Blizzard 'highly encourages' installing Diablo 3 early
In a move designed to create as smooth of a launch as possible, Blizzard will be unlocking the Diablo 3 installer before the game's May 15 release date.
In a launch day preparation guide, Blizzard confirmed they will be unlocking the game's installer at 8:01 a.m. PDT on May 14. This will allow you to begin installing the game, troubleshoot any issues you run into, download and install the launch day 1.0.1 patch, and be ready to play as soon as the servers come online.
If you've already purchased a digital copy of Diablo 3, you can get an even bigger head start and begin downloading your client right now which Blizzard "highly encourages" you to do so.
"As it may take you some time to download the full game, it’s best that you begin early," Blizzard suggested. "This may afford you additional time to troubleshoot any downloader or installer issues you may encounter."
In addition, Blizzard also "highly recommends" that you create your BattleTag now, if you haven't already. Remember, this non-unique nickname is a permanent choice, and will display both in-game and on the website, so be sure to choose one you like.