It's obvious that a large amount of time passes on Varys' journey. He leaves Mereen and sails for Sunspear in the same amount of time Olenna leaves Kings Landing and travels overland by carriage to Sunspear. Olenna has also presumably been in High Garden for some time to get word of Mace, Marge, and Loras, all before even receiving the summons from Elia. Varys secures the allegiance of House Martell, House Tyrell, and both fleets, sails back to Mereen, where all of them, plus the Greyjoys finally set sail. Months must have passed just between the scene of Daario telling Dany he's seen the people begin painting the sails, and the following scene when Dany is on the water.
What is not believable here though isn't the travel (or the editing), rather it's the logistics of cleaning up Slavers Bay after the boats in the harbor were torched by the Sons of the Harpy, then the battle in the Bay where the dragons torched several more. That cleanup would take YEARS given their technology.
Littlefinger going from the Vale, to Molestown, then back to the Vale, then to Winterfell is a reach. He's obviously got a Hearthstone or using Fast Travel.
Also, if Euron has one fucking boat that'll be a stretch, seeing as how he basically shows up out of the blue, murders a king, hijacks the Kingsmoot, then orders everyone to commit to backbreaking labor for the next several years... And I don't recall seeing even one tree on the Iron Islands in all those wide shots. Where are the Iron Born getting all this lumber, considering they don't trade and they don't sow?
