Keep us updated as they grow!
So far there are no indicators of the chick being a cockerel. Saddle and hackle feathers come much later. Red comb and wattles start at about 6 weeks old.
Slow and fast feathering genes are not linked to gender in australorps. That only happens if you cross breeds that have feathering linked to gender for either the male or female.
Yours are not crosses so the feather growth rate is moot.
I feather sexed the batch of 25 straight run hatchery birds I got at about 2 weeks, by tail and wings, and was 100% accurate. Maybe it depends on your source.