A standard torch burns for about one hour, shedding bright light out to 20 feet and dim light another 20 feet beyond. In open air or torchlit halls, it's enough to keep the dark at bay - barely.
Wind, moisture, and magic can shorten a torch's life, while careful hands and a shielded flame might make it last a little longer. DNs don't need to track every minute; let the torch serve as a narrative clock - a flickering countdown as shadows creep closer.
When that flame finally gutters out, the silence of the dark feels earned.