This really depends on what you're trying to accomplish. If you want off the dope, without just switching over to subs, you won't need much for detoxing from the dope. A local detox center where I am from switched over to using subs for withdrawal from opiates, like heroin. Their dosing schedule is:
Day 1: 2mg
Day 2: 1mg
Day3: 1mg
Day 4: 0.5mg
Day 5: 0.5mg
And that's it. For a whopping total of 5mg, for the entire detox. Which is just over half of a single sub. You obviously have a lot more than this, so it's what you decide to do.
If you plan on staying on the subs for longer than just getting you past heroins acute withdrawal, I would recommend starting at 2mg. If you still aren't feeling well enough after about an hour, keep moving up 2mg until you are. 4mg per day should be plenty. The transition, regardless of the dose, will probably be somewhat uncomfortable for a couple days. Don't let discomfort alone be the judge of how much you take.
Dope has a very short half life. But, I would still recommend waiting as long as possible before taking your first dose of sub. Around 24 hours should be enough. The longer, the better. Make sure you're feeling symptoms of heroin withdrawal first, then take your first dose of sub.
Good luck!