Michael was frantic to get Fredo on the plane with him that would take them out of Cuba. But, in the Vegas scene, after Tom tells Michael that he thinks Fredo's in NY, Michael simply tells Tom to get word to Fredo that he knew Roth misled him, etc. Since Michael was so anxious to get Fredo on the plane, probably less than 48 hours earlier, why didn't he order Tom to bring Fredo to him immediately? He waited until after his Senate appearance to tell Tom that he wanted to talk to Fredo.
Michael's head must have been spinning when he yelled at Fredo to get into the car. He was clearly devastated to realize that Fredo was the traitor. He doesn't know whether Roth is alive or dead. He is literally in the middle of a revolution without so much as a bodyguard. He surely hadn't had time to process and analyze Fredo's betrayal.
His reaction was probably a combination of thinking it would be wise to keep Fredo close and genuine concern for Fredo's safety.
By the time he gets to Nevada, he's had time to assess the situation. He knows Fredo is safe and that he poses no immediate threat to the Family. So he can afford to wait for Fredo to come back to him.
"A man in my position cannot afford to be made to look ridiculous!"
