The way I look at it is to look at Arteta. Took him until his 3rd full season, last season to improve Arsenal. He finished 8th in his first half season, 8th second season, 5th third season.
Fergie even took 4 seasons to win a trophy, FA cup, and he finished 11th and 13th in those first four seasons. He also had to clear out a lot of players.
Unless we are losing badly fairly regularly, when he has his injured players back, then he should be given the time.
We have sacked all the managers fairly quickly and rightly so, so far, but it hasnt made us any better long term. At least TH is trying from this season to bring in players that want to play for Utd and not for the paycheck.