I think the time travel is BS.
If Cap wasn't actually CHANGING timelines but just reintroducing the stones shortly AFTER they took them, then that means the actions they took during their Time Heist actually occurred. Which meant that Hydra thought that Captain America was part of Hydra or at the VERY least believes that Captain America knows about Hydra. Captain America would remember fighting himself (or Loki). Things would have already changed - which means that technically that universe is still in a branch, albeit a branch that had their infinity stones taken and then returned. There is NO WAY that Rogers should have been able to stay in that branch and then pop up in the timeline that Infinity War originally took place in.
I LOVED the movie so I'm not letting this ruin anything for me, but movies should just NOT DO TIME TRAVEL.