Answer:
Not knowing the specific kind of scan(s) that you need, it would be difficult to give you an exact answer to your question, to give you a general idea you can expect your MRI to take between 20-45 minutes typically. If you are having multiple areas imaged or are having a more intricate sequence done, it may take a little longer, but generally speaking 20-45 minutes is accurate.
Your scan will be broken into a number of different sequences which will typically last from one to several minutes in length. The technician who is performing your scan will talk you through the process so that you are aware when each new sequence is to begin and when you need to lay absolutely still.
You may find the following resource page that I linked to be helpful as it details what to expect from an MRI and also has a comprehensive 5 minute video which details a "real-life" scan.