"The best manager in the history of the Premier League needed a few years to build such a successful period," said Mourinho.
"If the best needed that time, it means that the others also need that time."
Ferguson arrived at United in 1986, but did not win a major trophy until he lifted the FA Cup in 1990, and it would be a further three years after that before he won his first Premier League title.
It would prove to be the catalyst for United to become the pre-eminent team in English football as they enjoyed a 20-year period of success.
During his 26 years at Old Trafford, Ferguson won 38 trophies, including 13 Premier League titles, five FA Cups and two Champions League titles.
Mourinho only took over from Louis van Gaal in May and speaking ahead of United's Europa League clash with Feyenoord, he said it may take time for his managerial skills to have an impact at the club.
"The job is as difficult as I was expecting," he told reporters at Old Trafford.
"I was not expecting the job was easy. I said that I wanted to try to win the Premier League, but at the same time I thought that was a risky approach with my words.
"My words were not defensive with the risk. I knew it was going to be very difficult."
United are currently sixth in the Premier League table, nine points below leaders Chelsea.
Mourinho revealed he has ambitions to manage United beyond his current three-year contract, but knows performances on the pitch must warrant it.
"I am in the beginning of my contract. I am in the beginning of the process. Let's go step by step," explained the Portuguese.
"If you ask me would I like to be successful in these three years, would I like to stay here for more time than these three years, then yes.
"Because I am in the club that I want to be. So yes, I would love it. But I have also to deserve that.
"Let us see the evolution of my result. And if one day the club thinks I deserve (it), then I will be very happy and proud about that. I am just in the beginning."
Mourinho accepts, though, that United fans will expect him to put some silverware in the cabinet sooner rather than later, although he is focused on putting his imprint on the squad.
"The three-year contract I was given is a fair period of time to give to me to where we want to be," he said. "Three years is not just about the transfer window, though.
"It's not just about that. It's about my relationship with the players, my understanding of the player, the understanding of the players of my personality as a manager. A person's routines, dynamics of how they work.
"That's got to be key. It's all about that. But if you ask me if I am a waiting for my third year in the club to have good results, no, I am not waiting. I am going to immediately try to do my best to get results."
Mourinho gave short shrift to suggestions United might try to lure Lionel Messi to the club from Barcelona.
"Lionel Messi is every season the same story," he said. "Every season he is going to leave and he never does.
"I hope he never leaves. He belongs to Barcelona. The beautiful thing for him would be to start and finish at Barca."
United have no fresh injury concerns ahead of their clash with Feyenoord at Old Trafford, with defenders Chris Smalling (broken toe) and Eric Bailly (knee) and midfielder Marouane Fellaini (calf) all set to miss out.
Original source: Mourinho in it for the long haul at Man United