Have a look at the timing of the long distance coaches on some of the routes - perhaps the Greyhound Sydney to Brisbane running through Armidale if that is familiar territory for you. These coaches have to pay their own way - and their timing is set such that the operator thinks that they will maximise the difference between revenue (number of passengers and the fares they are willing to pay) and the cost associated with the service. While these services don't operate in a vacuum (they need to compete with other modes, including at the southern end the daylight rail services) I think it is pretty telling that they have chosen overnight timings, both ways, for that run.Indeed, and thanks for picking up on the Greyhound service to Brisbane via New England that runs overnight both northbound and southbound.
I will also highlight that Greyhound and Premier Motor Service both run overnight services from Sydney to Brisbane via the North Coast (see this, this, this and this); Firefly's daily Melbourne service is also an overnight trip (both ways).
Forgive me for indulging my centre-right brain, but I think the private sector is onto something here.
Premier also used to operate a service from Sydney to Melbourne via the South Coast and Gippsland that was overnight both southbound and northbound, but they canned it last year. Nevertheless, it was yet another example of private long-distance coaches in Australia operating overnight so the point stands.
I think that overnight decision reflects that for many people, the preferred time of travel is strongly influenced by when you need to be at your destination, or when you are available to leave your origin. If I am travelling after finishing a hard commitment such as work or school or whatever, the timing of the service that I want is one that leaves as soon as practical after I finish work or school or whatever. If I am travelling before a hard commitment, such as work or school or whatever, the timing of the service that I want is one that arrives as soon as practical before that hard commitment.Exactly.
What "soon as practical" means will depend on a number of things, including service reliability and the nature of the commitment (for example I would not plan to arrive in Sydney from the regions five minutes before a long haul international flight), and also on the preferences of the individual.
Some travellers may only have weak time commitments and will then prefer to travel when it is most comfortable for them. But if you've got weak time commitments then you are probably not working... which means they are probably travelling on a concession of some sort or are very fare sensitive. In terms of potential revenue, this group just fill seats - they are not your primary market.
Hard commitments are very much part of my consideration, which is why I emphasise morning arrivals and afternoon departures so people can use actually these trains to come to Sydney to actually do things.
EDIT: Included timetable links to back up claims of the various overnight coach runs.