I try to keep them to 12 months each, ending at the last day of a specific month. I’ve printed three books so far; you’d think the thickness of individual books would vary a lot per year, but for our group it seems the amount of chatting is constant :)
Ah okay, thanks. I'm thinking of doing something similar with a Hangouts group. You can use "Google Takeout" to export your entire Hangouts activities in JSON... so it looks like I'll need to do a bunch of my own parsing. It's a fantastic idea though!