Can QF JASA and Jetstar flight be put on one booking??

[extracta]

I would like to book a JASA with QF from TVL to DWN, followed 6 hours later by a cash paid Jetstar flight to SIN.

If I make two seperate bookings am I covered in case the first flight arrives late?

If I am better off booking on one booking can this be done online, through Qantas, or through a travel agent?