By my reckoning, Steven creates 9independant timelines.
4 perish at the Sea Shrine, all having used the Hourglass. Each of the timelines belonging to these Stevens is now Steven-less, as none of them have returned to their original timeline.
--1 "Original" Steven (Steven Classic): dies at the Shrine after destroying the Hourglass.
--3 "Band Member" Steven: all die at the Shrine. All Stevens seen in the Steven Civil War except for the one in the hoodie can be considered offshoots of these timelines.
2 are left in timelines where they have the Hourglass, but have not used it. These Stevens have no idea about the conflict that caused the Steven Civil War, and are unlikely to have gone back to the Sea Shrine. They may in fact just take the Hourglass back to Pearl, preventing any further time travelling.
--1 "Carwash" Steven: When Original Steven goes back the second time ("I wish I could go back and stop myself from stopping my dad."), he only takes the previous timetraveller (Band Member 2), not the Steven from that timeline.
--1 "Scooter" Steven: When Original Steven goes back to stop the band forming ("Don't start the band Steven! It will only tear us apart!"), he is attacked by the Band Members and escapes. This timeline's Steven is left confused.
3 are left in timelines where the Hourglass is destroyed before they can touch it. It is not out of the question that any of these Stevens is the "real" one: ie the one the series currently follows. We have seen no reference to the events of this episode since.
--1 "Gem Glow" Steven: This Steven only briefly witnesses Original Steven and the Band Members poof in and then out, before barfing on the beach on Cookie Cat's "grave."
--1 "Rose's Room" Steven: This Steven never sees his timetravelling doubles, as he parachutes from the quadruple bunkbed slide in the background. This Steven would have no knowledge of the Hourglass or the horrors surrounding it.
--1 "Sea Shrine" Steven (New Steven): This is most likely the Steven the series is currently following. He is wearing a hoodie in the Steven Civil War, and is the last Steven left standing. He goes on to play an awesome set with the Crystal Gems at Beach-A-Palooza.
This leaves us with an unsettling development: even if destroying the Hourglass erased any timeline in which is was used, we have 5 timelines. If it destroyed any timelines it had influenced, then we still have 3 timelines.
Additionally, the Original Timeline (Episodes 1-22) is now Steven-less.
The Gem Glow timeline (Episodes 1-current), the Rose's Room Timeline (Episodes 19-current) and the Sea Shrine Timeline (Episodes 22-current) are now completely seperate from the original, and all completely plausible as a "Main Timeline."
What could this MEAN?
(p.s. The Ocean Gem timeline is factually identical to the Main Timeline (whichever one that is), as Steven did not influence anything in this trip.)
An infinite amount. The Many Worlds Interpretation states that the universe splits itself into multiple universes to accomodate all possible outcomes. A single step Steven takes would have made hundreds, if not thousands, of other universes, each having a different outcome from the other.
I think everything Steven did with that hourglass was erased when the earliest version of it was smashed. There's only one timeline: The one in which the hourglass was destroyed before Steven had a chance to do anything with it. The extra Stevens all just reverted back to the Steven who never got to use it.