Sorry, hard panning is when soil is cultivated a few times to the same
depth( such as tilling at 8"), the layer just below the tilled area
becomes rock hard and restricts permeability and root growth. But
with a one time bed raising, and mostly veggies, that probably wont
concern you.

The soil doesnt freeze where I live, so soil prep can be done at any
time of the year. Optimally I like to till in compost and organic
fertilizer and let it sit for a month or two to let the compost "get
to know the soil", which attracts worms and other critters. This is
not necessary, but it seems to help.

Good luck,
Bryan