I think it was the right time for a top talented coach like Ruben amorim to join Manchester United and use his technical skills to be able to salvage Manchester United season. Manchester United's fans should understand that the club is in transition and it will take time for Ruben Amorim to be able to put the squad together. It will be years before they can compete for major trophies consistently.
I don't think it was the right time. He could have waited till the end of the season. That way he will have advantages, He would have more time to get to know his players and experiment during the pre-season and know how he's going to play.
He would have also had an opportunity to sign players since the transfer window would be open by then. He would have time to identify the players he wanted and the club would have tried to sign them, but now he couldn't sign any players and he had no time to experiment.
Everybody involved in the deal made very poor decisions. After Ten Hag was fired which was a good thing, Ruud van Nistelrooy was doing a good job, he drew 1 and won 2 matches, even though they were not tough matches, but he should have been allowed to stay for a while. What United could have done in my opinion was agreed on a deal with Amorin to take over at the end of the season.
Amorin shouldn't have left Sporting where he had a good thing going mid season also.
I believe the timing of Amorim’s arrival isn’t bad, the transfer window is just around the corner and he w already had the opportunity to be able to assess the squad and identify the necessary changes to strengthen the team. Amorim’s arrival at mid season allowed him to observe the players performance in competitive matches and make him to gradually implement his tactical philosophy. This period gave him time to analyze the club's strength and weakness, laying a solid foundation for long term success at the club.