pz1, that did the trick! I changed the timezone and voilà, the scheduled scene triggers when it's supposed to trigger. No delay, no lag.
My timezone was set to Etc/UTC by default and I didn't even think about looking for a timezone setting since the time in the Web UI was displaying the correct time. Thanks for pointing it out. I wouldn't have even looked at raspberrypi_ip:8084 since I didn't even know it was there :D