I think drops actually started Thursday this time.

I don't check Twitch every single day, so there have times when I didn't realize that drops were on until the last day (Sunday), which was a bit depressing. What made it really bad us that I follow a number of streamers on Twitch, and I get emails that say when they're starting ti stream-- although I don't check my email account multiple times a day, let alone once a day, so I might not see those email notifications until a few days after the fact-- and most ESO streamers are very good about putting the phrase "drops are on" at the beginning of the notification.

So following a few ESO streamers, allowing Twitch to send you notifications, and paying attention to those notifications is the most reliable way of being alerted to when drops are on.