Update from 5.7.3

I have a Team environment with 2 MSM760 (5.7.3) controllers and 80 430/466 AP's.

Not sure if this is possible, have not found any documentation to support it.  But maybe someone has experience with this. Like to update one controller at a time to reduce/eliminate downtime.  Is it possible to only update one controller at a time while keeping the environment online?  Can both controllers be online with different firmwares?  Can one be put in standby to be updated then all AP's migrated to it then do the other?

Thanks in advance