Pink noise is your friend here, place the speakers 1m apart facing each other, connect one of the speakers out of phase, feed a mono signal to the speakers, (Pink noise is ideal as it covers all frequency bands appropriately) you will then be able to turn up the volume loud (Just be careful not to overdrive the amp and speakers) without interfering with the neighbours as the sound cancellation will keep the sound low. (This is basically how noise cancelling works) NOTE: The volume from the speakers will not be low, it will only appear to be.
As to the amount of time, check in the manual as it is normally specified, if not then the manufacture has probably already done it at the factory so you can just sit back and enjoy.
Bill