How long do railroad fusees last or where can I find info on the time, like 5, 10,15 minutes?

10 minutes.

In the good ol' days, if a train in "dark territory" (operating with no block signals) couldn't make maximum authorized track speed, the brakeman or conductor on the rear of the train dropped fusees at ten minute intervals. This was done to insure following trains didn't overtake and rear end the slower train ahead.

You should get some bonus points for calling it a "fusee", which is the proper term, instead of "flare".

All railroads fusees last 10 minutes. FYI. CN Rail has a 6in. spike in the bottom of the fusee, you can stick it in the tie upright, in the snow...

They last until the have a current greater than what they are rated for passes through them. Them they blow, same as any other fuses.