I think it's reasonable to expect that the staff involved in an emergency callout of this sort will be entitled to Time Off In Lieu, and that that TOIL will cause knock-on effects to staff rostering.

Delaying the inspection until working hours would have caused much greater disruption. Having a track inspection team on hand 24x7 to cover all potential routes would incur much higher staffing costs.

An on-call system backed by TOIL and accepting the risk of dealing with occasional re-rostering seems like a reasonable compromise to me.