Can I transfer to the train from the bus on my third fair?

I'm a NYC student and I use the student metro that has 3 fairs. So basically, I take the A train in the morning to school at 66th St Lincoln Center (one fair). That's all I need. But I'm going to Queens Center Mall soon so I'm going to use the M (another fair) and to come home with the Q21 bus (third fair) and I need to transfer to the A train again going uptown (that's already a 4th fair?) I don't really know how this works. Can I transfer from bus to train after a 20 minute period so all together it'll be a only 1 fair? Because it only takes me 20 minutes with the Q21 bus to reach the A train at Rockaway Blvd.