SpaceX is targeting 11:30pm EDT launch on June 24, 2019 for their 3rd Falcon Heavy mission. The two side boosters previous flew on the Arabsat-6A mission back in April. Backup windows open at the same time on June 25th and June 26th.
This will be one of the most complex missions SpaceX has ever flown. The Falcon Heavy rocket will attempt to deliver 24 separate spacecraft from a variety of commercial, national, and international partners. These spacecraft are targeting three different orbits and using 20 commanded deployment actions. While the previous Starlink launch on Falcon 9 delivered 60 spacecraft, they were all delivered to the same orbit.
More information can be found in the SpaceX press kit: https://www.spacex.com/sites/spacex/files/stp-2_press_kit.pdf