I tried setting up a similar schedule, and while I’m not really familiar with hour intervals, it looks to me that:
When setting up an hourly interval, it will water EVERY day the same HOURLY interval, continuously. That is, let’s say it starts at 8AM tomorrow. It will water at 8 AM, then 12 noon, then 4 pm, then 8 pm, then midnight, then 4 am, then 8 am, etc. CONTINUOUSLY. So at least after day 1, the Start time means nothing. It waters 24 hours per day at the hourly interval selected.
Now, while it /should/ start tomorrow at 8, if tomorrow is the start date and time, it seems to ignore the starting time, determining that basically any day it should water, it needs to water every 4 hours, starting at 8, but the previous day will continue until 8 the current day. In other words, once set, starting on the day you say to start, it will water every 4 hours continuously, and one of those watering times will occur at your 8 am.
Now, that does sound just a bit screwy, but in fact the default start date for all schedules is yesterday, so unless set otherwise, it’s going to start right away. And you want to water every 4 hours, and that’s what it’s doing.
I don’t believe there’s a way to use a hour duration that is NOT continuous, all through the day and night. You could set up any number of Fixed schedules, one for 8 am, one for noon, one for 4 pm (and ore if you want), or you can play around with fixed soaking times, which can get a bit confusing, especially with multiple zones.