On Origin before the rest of the shards received the most recent publish, the putrid undead gargoyles were spawning for 30 minutes out of each hour of RL time. They spawned from 7 am to 1 pm shard time and 7 pm to 1 am shard time. I have not checked any other shards since the rest of them received the publish to see if that same schedule carried through to all of them, but I suspect that it did. You can buy a clock from a tinker NPC for about 22 gold. Be sure to check the time while in Ter Mur. There seem to be a few areas in the game where the clock will give you a different time than what it is in Ter Mur (e.g., in Luna and maybe some other areas of Malas).