If you are on the QF flight SYd-NRT, you'd have all day to travel up from CBR.
Not if it is a day I'm at work. Only way I can get to SYD in time to get on QF21 is on QF806 or QF1494, and even then I'd have to get out of work early. (asking for one less day off can make the difference in the leave getting approved)