how long do you think it would be travel from Jacksonville Florida to Australia?

Depends on how you are traveling?

It will depend upon where you want to fly to in Australia. If for example you want to arrive in Sydney, then according to this link
http://www.expedia.com/pub/agent.dll?tovr=-1294677295&ps3u=
it would take 33hr 25mins to fly from JAX to Sydney with connecting flight.
As a comparison, it takes about 13-14hrs to fly to Brisbane direct from LAX. Therefore you could select a city with direct flights to Australian cities and leave from one of those.
Hope this helps.