Flight changed to a more inconvenient one prior to takeoff

I bought flights to Melbourne last night for a flight departing in November scheduled to take off in the afternoon. This afternoon I received an email saying they have changed my flight to one at a different time which is really early in the morning. The time difference between the two flights is ~6 hours. Since the airport in Melbourne is quite a trek it would mean I would have to get up super early to get there.
I specifically booked the more convenient flight for this reason.

They have not said the reason for the change of flights, but I presume it’s because it has been overbooked. They have given me the option of a refund or accepting these new flights. I don’t really want a refund because I have to get home. There aren’t any other options that day or the next day apart from Jetstar which is quite a bit of a downgrade.

I had a look on their website and it’s a bit unclear about this particular situation. Their examples are mainly around what happens when you can’t make a flight and not them changing it from under you.

Do I have any recourse to get my flight switched back to the original or to get some sort of compensation for this?
What would be my best course of action? Email
them and ask why my flight was changed?

I should also add that I haven’t purchased travel insurance as I only booked the flights yesterday and was going to purchase it closer to the time.