Justin Timberlake and his ex Jessica Biel went on a date over the weekend that was so secret, they wore masks. They went to “Sleep No More,” the interactive Chelsea play that crosses “Macbeth,” a haunted house and a costume party, and provides masks for all guests. Timberlake and Biel have been spending time together and “taking things slowly,” according to reports, after ending their four-year relationship in March. Reps for Timberlake and Biel did not return calls.