The preseason schedule has been released by the NFL. And the Dolphins do have a nationally televised preseason game. The team's 3rd preseason game at Tampa against the Bucs will be on Thursday, August 27 and televised nationally on FOX. That's especially great because the 3rd preseason game is typically the game where the starters play the longest.
The Dolphins other 3 preseason games do not have dates and times yet. Below is what we do know:
Aug. 13-17: Jaguars at Dolphins
Aug. 20-24: Panthers at Dolphins
Aug. 27: Dolphins at Bucs (8 pm EST)
Sep. 3-4: Dolphins at Saints