Have you ever noticed that the CG constantly somehow know where Steven is? Like in...
- warp tour, they somehow knew he was in the warp stream.
- catch and release, they somehow knew that Steven was at the galaxy warp. I mean he couldn't have gone for more than ten minutes at most and barely made any noise.
- when it rains, they somehow knew he was at the kindergarten, but somehow without peridot (amethyst and Pearl were both surprised that peridot was with him). They couldn't have been gone more than half an hour.
I know that you can argue that garnet has future vision but if that is true then why does she not know stuff like the cluster being peridot's mission, peridot being freed, or the location of malachite? Another thing you can argue is that Pearl watches Steven sleep but he wasn't sleeping yet.
I know it's a common tv trope that the children, like 7 year olds, freely walk around a crime ridden town without supervision. But there's times where the gems don't show up. Like the island adventure (although in all honesty I think maybe Steven said he was going to the island for a few days).
It's not immediate, seeing back to When it Rains, it took awhile for the Crystal Gems to arrive. Steven had summoned a bubble and was holding the gem mutants off before they came. I think it's safe to say that Garnet's future vision is trustworthy.