It's not a problem in Darwin. The AIP says:
--(by night) maintain an altitude not less than the route segment LSALT/MSA or appropriate step of DME/GPS arrival procedure or 500FT
Thus when cleared for a visual at night, and within 25nm you can descend to the MSA (1600' in Darwin). This ties in nicely with the 5.28 NM circling area. 1600' with about 5nm to run --- perfect.