Well, I can reproduce your issue without the patch by temporarily
changing my timezone to GMT+10 (TZ=":Etc/GMT+10"), and the branch does
fix it. It's merged to master now.
I tested as follows after activating the compile-time super-realtime
debug mode (can't be bothered to wait 24 hours when testing things):
TZ=":Etc/GMT+10" ./build/wlsunset -S 6:00 -s 20:00 -d 3600 -t 2800