I'm glad you brought this up Adrian. As I'm doin something similar with my Clam tank.

Lighting is a 400 watt 12K along with 96 watt PC 10K so I too was worried about Heat. So my time sched is

4am to 8am MH
4pm to 10pm PC

Using the pc lighting along side my 210 which is also powered by PCs from 4pm to 10pm (just so the color isn't offset by the MH)