They do not share spawn timers and they all seem to be on fairly similar timers which range somewhere in the 30min to 2hr + range.
Here is a map where all of their spawn points/patrol areas are. ~
|Click map to enlarge|
|7:XT, Barnabus & Rumbler|
|War Golem, Broken Tooth & Shadowforge Commander|
|Anathemus, Barricade & Zaricotl|