Should I start planting now

I want to plant lily pily as soon as possible so they can grow tall to form hedge over a fence.

My choices are either 200mm pots for like $25 and planting them now but I’m worried about the heat.

Or I could wait until autumn and plant 300mm pots that are bigger but they are like $80 each and probably more risk transplanting mature trees. Also prefer not digging a much bigger hole.