I would plant them anytime now. They do best germinating in warmish soil and growing in cool conditions. Spacing isn't too important, I generally sow seed about 1" apart and forget to thin. A friend spaces them 6-8" apart. The closer the spacing the sturdier the trellis/support system needs to be. I used 4' t-posts and twine run from one to the next. They grew over the top twine and stretched it such that they were able to flop over. My buddy did the same thing, but used chicken wire fencing and it held up fine.

I planted mine 2 weeks ago and they are 2" tall already, so go for it.

I'm resurrecting this thread in the hopes that there will be more advice for fall peas.

I think sometime within the next month should be the planting time for fall peas, right?