Reading through JAL's posted flight menus and my photos, the midflight snack is only for PE and ice cream is served both directions as dessert for both PE & Y.

I've only done one trip since JL1/2 switched to daytime flights. To HND, CA served the katsu sandwiches from a tray. My photo timestamp shows it was about 7 hours after takeoff. I was napping on and off so it may have been available earlier or on demand. To SFO, I'm not sure when the midflight snack (boxed doriyaki) was handed out.