a static respawn time was a primitive solution, because now people can just set a timer and come back
a better spin on this is a lotto spawn, have the field of monsters there you have to kill and a chance of it respawning as a boss when you kill it, on top of a randomized respawn time for the boss
this would spin off anyone who plans to just camp this same monster and hold a monopoly over the single item
no one likes people sitting and waiting for a boss, its like sitting out camping for the wii, no one likes it but those die-hard fans would want to get their hands on it first