You will have to meet them after they come out. into the open area downstairs.
Aust immi zones, out and in, are on separate levels.
You can wave at each other, near the pandas, if you know where I mean.
Once you go into the immi sec zone, its one level separation.
Arr, also one level separation.
Tullamarine is not like SIN Changi, when inc and out going pax can meet.
Don't believe me, give it a try and see.
They (inc pax) might come out from zone A or Zone B, after immi & DAFF checks, and you can meet them downstairs, before you go upstairs and do out immi and sec screening.
Different if friends are on transit also to HKG tho.
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If the friends get inc immi processed by 11pm/23.00 (or earlier), that will still give you enough time to go upstairs, and do out immi by say, 11.45pm/23.45, it will be a tight run to the gate, but all depends on when the friends get out into the open zone.