Quick Googling, I can't find a definitive answer, or any answer, really. Someone should test it out! Suffice to say the basic campfire lasts a long time, longer than the average grind camp, methinks. The special campfires are a lot shorter-lived, such that I stopped using them because the buffs they provide now are pretty trivial and I stopped counting how many times after a wipe I tried to click back to the campfire only to discover it had burned out unbeknownst to me. Special campfires are another one of many older EQ features which should be upgraded but never will be.
Sippin 105 DRU *** Max AA *** Firionia Vie
Master Artisan (300) * Baker * Brewer * Fletcher * Jeweler * Potter * Researcher * Smith * Tailor
My crew: 105 WAR ENC CLE MAG WIZ 100 SHD BER RNG PAL SHM Master Alchemist *** 85 ROG Master Tinkerer & Poison-Maker