While I don't have experience with seedballs using acorns,
I have had much sucess with planting acorns directly.
Depending on what type of oak you have, ... the treatment varies.
According to my information, oaks from the Black/Red family must be
stratified, while oaks from the white family do not. This does make
sense in terms of the requirement to leach out some of the tanins in
the Black/red family, but I'm not sure that white is completely free
of the need for stratifying.
There maybe scrub oaks that can stand drying out, the oaks around
here atleast, cannot dry out or they lose they're fertility rapidly.
They are meant to be buried by squirrels and the like immediately
after falling to avoid this drying out.
I store mine in the fridge in a bowl with a little bit of water
about 1" (2cm). I roll it around to coat all the acorns every ten
days or so.
Acorns usually take a long time to sprout, as the water has to
penetrate the outer shell and make it soft enough, and allow enough
water for the acorn seed to germinate.
Generally the first couple of weeks (2-3+) the acorn sends a tap
root strait down (this is what gives oaks better drought protection
than most other trees), This is the stage I like to plant them.
After sprouting, before leaf out.
There are two methods I've used for planting.
The first is to spread them out, and cover with 2-4" of compost
(leaf rich compost works better),
the second involves using a stick or a dibble to punch a hole in the
ground and dropping the acorn in that. then closing the hole up with
1"-2" is ideal planting depth.
While I've never worked with seedballs for acorns, they present a
couple of problems: the drying out, the lack of soil contact once
the tap root breaks outside of the shell , this would leave the
taproot vulnerable to sun, and drying out further.
If you do go with seedballs, I would try a much larger variant,
baseball size (3-4" diameter). Reduce the amount of clay, to just
enough to hold the thing together.