Not necessarily to save time, the first one was because Captain Marvel was a late entry and they had to shoehorn her into the plot somehow. All her appearances in that movie had an alternate and more cohesive way It could have went, such as Stark and Nebula finishing the rudimentary repairs they were seen doing and limping home on their own power.

Time travel was also mentioned in the Ant-Man and the Wasp stinger, so it didn't completely come out of nowhere. Stark didn't invent it, he invented a navigation system.