MAN did previously use an airside connection. Even this page suggests it did
https://www.manchesterairport.co.uk/...ked-questions/

However it now only links to a page which details transfers that are landslide. I wonder if this is to do with the current building works?

55 minutes should certainly be doable as the distances between the terminals is fairly short. However, this will depend entirely on security in T3. Ask any regular and they have very much the same impression of this. It’s awful. Even fast track is slow as it shares a lane at the scanner with ordinary passengers. Even on a good day I would expect at least 10-15 minutes and just hope you don’t get secondary.