Michael was frantic to get Fredo with him on the plane out of Havana. We can understand why.
Yes, because he was his brother, and Michael loved him and wanted to protect him.

Seriously though I don't think it was a
100% sense of urgency in the sense that Michael wanted to keep Fredo under his watch at that very moment. It was a combination of things. I really believe that while a sense of urgency in wanting to keep Fredo close to him to get information out of him did play a part in that scene, I also believe that a percentage of his brotherly instincts, as well as his being the head of the family instincts came into play at that very moment in that he realized that Cuba was about to be taken over and that he needed to get his mother's son out of there unharmed. Smart enough to realize that there was information that he needed to get out of Fredo but at the same time instinctively looking to protect his brother from what was about to take place in Cuba.
But, in the 48 hours or less that it took him to get from Havana to Vegas, his sense of urgency disappeared.....
.......he doesn't say, "Find him and bring him here immediately." Why did Michael lose his sense of urgency in grilling Fredo? I'm hoping people here will have other theories
I believe that Michael wanted to make it appear to Fredo that everything was ok, that nothing was going to happen to him and that Michael was no longer mad with him.
Michael lost his sense of urgency because at that point he was not yet aware that Roth had gone with plan B, the senate hearings. Not yet aware that Pentangeli was still alive, that both he and Cicci would be made to testify against him.
2. How did Fredo know "they got Pentangeli--I can tell you that," when Tom and Michael hadn't known until just before that scene?
Perhaps while Fredo was "hiding out" in New York, he heard things. Heard rumors that Frankie was still alive and in custody. Which goes to show that Fredo may have once again been a bit negligent in that he didn't inform Michael of this rumor ahead of time, just as he never told Michael about Questat belonging to Roth before Michael confronted him in the boathouse.
The more I think of these things, the more I am beginning to think that Michael was justified in having Fredo killed after all.
3. Fredo tells Michael, "That Senate lawyer, Questadt, belongs to Roth." That seemed to come as a complete surprise to Micahael. How did Fredo know that? Again, I doubt that Roth would have told him any more than he would have told him Pentangeli survived--Fredo by that time was useless to Roth, and and Roth would never have trusted a dunce like Fredo with any such valuable info at any time.
Your thoughts?
I would have to specualte that Fredo, when bouncing around those places that "Old Man JOHNNY knows like the back of his hand," must have been in the company of Questat and other politicians who were being shown a good time by Johnny, ones that Roth had in his side pocket.