8.3 seconds according to the Zapruder film. The first shot starts the clock. There’s guys on YouTube who easily do it.
8.3 seconds would allow enough time for 3 shots. And I do give more credence to the Zapruder film than an open mike recording. They obviously don't correspond, but I just wonder what noise was captured in the recording, because it sounded like 3 evenly timed gunshots within about 2 seconds.