Fantastic!
I think tzselect doesn’t actually “select the timezone” despite the name. It’s a utility to see what the time would be in other timezones.
It occurs to me that this could have been avoided if the time on the front web page actually showed the fully configured local time. Right now the sprinklers program sends UTC time to the browser, and the browser converts that to local time. What I SHOULD be doing is converting to local time in the program and sending that to the browser. That way it will be very obvious that the timezone is messed up on the raspberrypi right from the front page.