I didn't hear any pings -- that's how my parents always tested their preserves -- but the recipe said to wait until the jars had cooled to room temperature, and then check if the lids flexed when gently pressed, or stayed down.
Mine are staying down, but I put them in the freezer, just to be safe. They cooled overnight, so I doubt the jars will crack in the freezer.
I liked the taste of the few spoonfuls left in the pot, but overall this was a complete pain to do solo. My parents always did the work together, press-ganging any kid old enough to reach the stove to peel and chop fruit, stir the pot, etc. There were several occasions last night where I was wishing for an extra pair of hands.
Meanwhile, my friend who organised this has made noises about how peach jam is insufficiently exotic or something. I love peach jam, so I'm thinking I'll just keep it for myself and forego the swap. That way I'm the only one who has to deal with the jam, and I don't have to worry about other people.
I've made on-purpose freezer jam before, and I like cooking, but this is something else again.