According to this post: http://elitistjerks.com/f79/t92983-team_robot_simulator_gear_comparison_tool/p2/#post1576006
 
"Our default rotation uses Searing Totem, because our tests show it doing equal or slightly more DPS than Magma Totem. (The totem itself does a bit less damage, but it frees up extra time to use other abilities because you have to cast it less often). EnhSim (I was using version 1.9.7.1) doesn't seem to model Searing Totem very well. It always clips out 1 minute of up-time (one cast) that it should not. For instance, in a 5-minute fight using Fire Elemental, you should see nearly 60% up-time for Searing Totem, but EnhSim shows 40%. For a 7-minute fight, it shows around 57% up-time when it should show 71%, and so on. If I just manually correct for this bug (by multiplying the DPS done by searing totem appropriately), EnhSim also shows Searing Totem to do slightly more DPS than Magma Totem."
 
There appears to be a potential bug with searing totem uptime. In a 5 minute and 7 minute fight with 0 variance, EnhSim does indeed seem to be clipping off ~1 minute (or 1 cast, 40% uptime [compared to 60% normal] for a 5 minute fight, and 57% compared to 67% needed on a 7 minute fight). I cannot tell if it is doing the same for fights with variance (though I would imagine it is, I am not good enough with the code to tell).