I don't know if there is any official canon on Thanos waiting, but no doubt about it, the writers had to do something to Asgard and Odin before Thanos made his move there. How would Thanos and the Black Order have feared invading Asgard I wonder?... even with the Power Stone in hand... Sadly also, aside from Odin's intervention with the Frost Giants at the beginning of Thor we never really saw enough of his overall power. The writers have always managed to keep the Thor movies about Thor, which is to be expected I guess. You can't just keep throwing in movie storylines and plots like you can comics.
Malekith did not have any fear or issues invading Asgard (yes i know bad movie).
I did find the reason for him waiting.......
"That, according to McFeely in the commentary, was “the catalyst for the whole movie.” Having “figured out where the Soul Stone was because he captured Nebula on his ship and rooted around in her brain and found out that Gamora knew where the Soul Stone was,” Thanos is inspired to finally make his play for universal domination.
But why? In the commentary, Joe Russo explained further: “The reason why [Thanos] has not gone after the stones before is because the minute he does, the forces of the universe are gonna line up against him. If he doesn’t know where the Soul Stone is, then what is the point.”
In other words, if the people of the universe were tipped off to the fact that the big scary guy with a huge army was seeking godlike power, they could have mobilized to beat him. So, when he acted openly, he needed accomplish his aims as quickly as possible. Thanos might be incredibly powerful after all, but he’s not invincible, and neither are the armies and lieutenants who serve him – the longer it takes him to find all six stones, the more time there is for his enemies to stop him. Which is why he preferred to use proxies before now.
And until he knew the location of the Soul Stone, that necessary quickness wasn’t an option".
Mine arrives Friday - can't wait!
