
Select births, and accept the default option "no" re the search by reference no.
Use the wildcard option for the surname.
So use the asterisk (uppercase 8 on standard keyboards)
do NOT enter any other options re names
Scroll down to Date of Event
from and enter 11 01 1883
to and enter 13 01 1883
(notice it does not like entering same date at both options)
THEN if that does not turn up any likely results, consider that the birth registration has perhaps not been included in the online index.
ADD
NSW BDM online allows you to select a heading on those results and re-sort to that heading.... so you could select Armidale or Newcastle

after obtaining all the births registered at the Head Office of the NSW Registrar General

(Don't forget that in 1883 that births were registered locally and the deputy BDM registrar was meant to forward those registrations quarterly to Sydney HQ and that there was no formal regulations ensuring that quarterly process actually occurred until after WWI ! )
Cheers, JM