Are you eating them whole and with the coating, or crushing up to destroy the time release? This would really influence when to take it.
Also, are you willing to go to a suboxone clinic? They are usually decently priced, and a doctor can help you in taking your first few doses, as well as helping you be comfortable. This is really what I would recommend. Just bite the bullet and do it, so it is safe and under a good medical setting.
If not, I would wait until your withdrawals are pretty much hell. I'd say at least 24, but I am not a doctor or anything so don't base your decision solely on my comment. It is gonna suck (it always will), but I have heard things of it making your withdrawals much worse if you are only in mild withdrawals. Also, you don't want to die taking opiates too close together just trying to get clean. 8mg is a pretty high dose from what I can tell, usually most addicts are started on 4mg, and taken throughout the day.
Sorry I can't help too much because I have never used the substance, this was just from researching around the net, and word of mouth from friends to try to help. Be safe, and good luck with your withdrawals.