Yes Mason Mount needed some time to adapt to Ten Hag's style of play, which is natural considering he needs support and I think what is really important is the emotional connection between the players. As the opening match of the pre-season, Man United won through their academy players. This is also an opportunity for their young players to show their quality and hard work in order to break into the main squad.
I don't think Mason Mount need long time adapt with Eric Tan Hag game style, almost all Primer League team has the same character games play with counter attack. Mount career only in Primer League with Chelsea and actually he understands well how need strong phsycal in the field. But has possibilities with Mount get new position between move up as attacking midfielder or holding midfielder.
He must fighting with Bruno Fernandez if want get regular position as attacking midfielder but possibilities with Mount as partner for Casemiro on holding midfielder. Before accepting Manchester United proposal, seems Mount know about get regular position or not.