It's quite easy, I'd say 2 weeks to finish and understand the content plus another 2 weeks looking at exams. You can of course shorten it by a week if you put in more time but I'd say 4 weeks, although 3 weeks is possible with strong dedication.
I wouldn't listen to half the answers here. When you learn S1 you have to be able to apply all the knowledge you have gained and recalll everything in months time, so for someone to learn S1 in a week means they were not spending adequate time on each section and doing practice questions. However if you did then congratz to you. I'd say it would take a month to fully understand the concepts and apply them later.
I got taught S1 and S2, but I self-taught S3 - that took me about two hours a day over the Easter holidays, so two weeks (I was revising all my other modules as well). I wouldn't agree with the other people saying that you need a month to fully understand the concepts - I did a lot worse in S3 than my other modules, which were all around 97 UMS, but I still got a mid B in it. So I would say two weeks should work for S1 too. Obviously, the more time you have free to spend on it, the better the grade you'll get, but if you don't have much free time, don't worry!
I got taught S1 and S2, but I self-taught S3 - that took me about two hours a day over the Easter holidays, so two weeks (I was revising all my other modules as well). I wouldn't agree with the other people saying that you need a month to fully understand the concepts - I did a lot worse in S3 than my other modules, which were all around 97 UMS, but I still got a mid B in it. So I would say two weeks should work for A1 too. Obviously, the more time you have free to spend on it, the better the grade you'll get, but if you don't have much free time, don't worry!