I accidently made my road flare last up to an hour (before I needed to logout).
It seems this can be triggered by switching server while a burning road flare is still in your hands.

During the session where it lasted over an hour, I needed to leave the flare several times on the ground to fight infected or craft items. Other times when I've done this, while keeping to one server, the flare was consumed in about 15-20 minutes.

Version 1.0 stable on two servers (without mods)