The timelines progress as normal, but Steve is time-travelling back again to replace the stones.

The question of making double splinters in the timeline by going to return the stones is one of the reasons I think the Russos are wrong and Markus & McFeely are right: it's not the time travel itself that causes splinter timelines, it's the going back and removing an Infinity Stone (as mentioned by the Ancient One). Which would mean Steve didn't create a new timeline when he went back to 1949, and lived out his life in the MCU.

But if you ask the Russos, each trip in time does create a branch, and Steve created a branch. Which opens up a tonne of questions they haven't answered.

That's the huge problem with Endgame... the time travel logic in both M&M and the Russos perspective has serious flaws, that put their logic in jeopardy.

I think this has already been discussed, by myself included, and I think I should rather retract from exposing all of the issues that exist with Endgame's time travel, as I think the most avid users in this discussion area are aware anyway regardless.

Just a little bit of a feedback to what you said regarding Tony's funeral being set a day after the Battle of Earth (although you did say "at least a day after"), the wikia's timeline dates Tony's funeral as being 12 days after the battle. Either way, that shouldn't have no problem in the task of retrieving the stones back to the past, as the point is that you can go to the past at anytime and in any timeline you want, and Steve returns the stones at the exact same moment they were removed from that timeline.

Yeah it's 12 days due to things like Peter and Ned going back to school between the Battle of Earth and the funeral, which wouldn't just happen instantaneously after an event like the Blip.

Agents of shield explained it well (when you travel to the past u don’t branch unless u change something that happened originally - Hulk stated that as well , he said CHANGING THE PAST DOESN’T CHANGE THE FUTURE(didn’t say time travelling its-self)

, that’s why there are timeloops that happened in agents of shield in the finale and in Avengers Endgame when Captain America returned the stones)

The issue that supports the casual timeloops in endgame is that if steve messed up in any timeline while returning the stones he will create a third timeline, so messing up the multiple timelines ( the one created when they took the stones and the new one created by the change that happened when cap was returning the stones)

That’s why Hulk kept reminding Steve to enter the timelines at the exact moments the stones were taken

And probably Steve staying in the past was a loop as well ( the loop theory explains the confusing issues about him not returning through the tunnel )

I think Loki is going to explain the time travel things - mainly the loops- to the people who didn’t watch agents of shield by making Loki DB cooper

When Banner talks to the Ancient One he explicitly says that they will bring the stones back to EXACTLY where they pick them up, so the basic answer is that no time will have elapsed. Just like when the characters were done with their respective missions they all came back to the same time in the present, despite the Soul Stone requiring a much longer trip through apace and however long theh debated and then fought, and War Machine leaving before Nebula is captured and tortured. They all reappear at the same time because they set the time beforehand. Hulks machine at the end is designed to take Steve to exact times again, and that's why he mentions Steve blowing right past his "time stamp". That's the term they're using for the exact moment they've allocated for the travel to.