Learn to read/understand the NOTAM for various areas as at times some of them can be "deactivated" where RPA flight would be allowed without prior approval.
Second to this is paying attention to the flight levels of the NOTAM, I've seen instances where a NOTAM will be in place, but does't take effect until 1000ft AMSL, meaning SFC to 1000ft the airspace is "clear" for use.
In either situation you still need to be on your toes/eyes/ears for any potential manned flights that do not have ADS-B tracking, which for a lot of craft this is "the norm" and not mandated by CASA.
EDIT: it's the "Restricted Area Briefing" that you'll find of most use in conjunction with OpenSky app to advise of the area code (R421A as example for an area in Nowra).
I can see for the week in that area there is a NOTAM:
C0119/20 NOTAMN
Q) YMMM/QRRCA/IV/BO/W/000/125/3458S15035E050
A) NWX
B) 2009070000 C) 2009110430
D) 2009070000 TO 2009071300
2009080000 TO 2009081300
2009090000 TO 2009091300
2009100000 TO 2009101300
2009102200 TO 2009110430
E) R421A ACT (RA1)
F) SFC G) FL125
The above times are UTC (UK/London time) so we need to convert them to our applicable timezone.
They read as: YY MM DD TTTT
B) 20 09 07 0000 C) 20 09 11 0430
20 Sep 7th midnight TO 20 Sep 11 4:30am UTC
20 Sep 7th 9am AEST TO 20 Sep 11 1:30pm AEST
If the need to fly within the B and C dates is required you need to pick through all the times specified on the NOTAM to confirm if there is any daylight hours where the area is deactivated from restricted use...
Otherwise it appears the NOTAM finishes on 1:30pm local time on Friday 11th... which would mean that afternoon you'd have clearance for that area.. Note you need to refer to OpenSky to confirm where that R421A area geographically applies to.
Also SFC = surface = ground - FL125 = 12,500ft