I often see only 1 update per day, but sometimes I see 2 different results on the same day. What time do they get updated?

Don't know how often BOINCSTATS polls the different projects. CPDN stats on the whole only get updated once a week. Less often when the script to update them doesn't start for some reason so it doesn't run till a cruncher posts about it and a moderator informs the project.

Each project publishes its own stats, usually once or twice per day but sometimes more, sometimes less. It's configurable. The timing usually starts on the 24 hour or 12 hour anniversaries of the last time the project servers were restarted - so it's effectively random.

Each of the many statistical aggregation sites will have their own policies and timetables. Probably the best known, https://www.boincstats.com/, polls the projects throughout the day, and collects any new data available. Incremental updates are posted whenever available in the 'today' column, but the definitive 'Credit/Day' total is usually published in the afternoon, UTC.