Overwatch will be heading into its final beta event weekend beginning on Friday, April 15th at 9:00 am Pacific / 12:00 pm Eastern and running through Saturday, April 16th at the same times. All eligible accounts will be flagged in the afternoon of April 14th to allow time to download and install the beta client.
If you're selected to participate in this Beta Test Weekend, you'll see an Install button appear in the Overwatch tab of your Battle.net desktop app as well as an Overwatch Beta license in the YOUR GAME ACCOUNTS section of Battle.net Account Management.
This weekend's event till give players access to all heroes and several maps including Hanamura, Route 66 and Nepal. Weekly Brawl and Competitive Play will not be functional during the event.
You can read the full announcement on the Overwatch site.