So my real question is, how long will this take to heal up and look nice?
How long is a piece of string karl? the time for this to heal will depend on so much - how well you grow it, whether you allow free growth or restrict it, pot/ground, where you are, etc, etc.
My callistemons grow quite quickly and heal well. I found i had to keep widening the shari on my waterswept callistemon because it kept threatening to heal over.
I would make the sloping cut in the final position now then keep pumping feed and water into it and allow a bit of growth - note growth does not have to be one long shoot. Thickening depends on NUMBER OF LEAVES (or more importantly leaf area) not height of the shoot so even regularly pruned leaders that produce plenty of side shoots can cause effective thickening/ healing.
With rough bark like that one has the scar should be un noticeable soon after it does heal.
Also note that I have done trials and i am convinced that sealed cuts heal over far quicker than those left bare.