On my server, at least, the reset time of all heroic instances is 11:00 AM CST (it is a PST server, so I'm two hours behind it). That gave me time to run two of them prior to 11am, then the other two after that.

Now that tankadins don't run out of mana every 1-2 fights, OHB and BM sound more reasonable to me on heroic mode. Never tried either in heroic though. Mana Tombs I've held off on due to the claim that you need something like 200 shadow resist for Pandemonius (though the tankadin would give 70).