I’m on PST too and have had notices from IRCC as late as 4 sometimes. My very first work permit was approved at 5:30 a few years ago. I don’t think there’s any rhyme or reason to it. Sometimes I wonder if there’s activity and we get some sort of auto notification a bit later.The latest I've heard is 2pm EST.
I'm in PST and I lose hope for the day at noon haha.