Idk what time zone you are in so when you say 3pm yesterday idk how long it has been. Coke should not have any effect whatsoever on the suboxone.
The general rule of thumb is to wait until you are in full WD or about 18-24hrs. I would wait as long as you possibly can. Only do 18hrs if you are 100% you are fully sick. Cause if you aren't trust me, its going to be 10x worse than how you already feel. So its not worth doing it an hour or two early if you aren't sure.
But yes, I'd start off with 1-2mg and wait an hour or so (2 if you can) then at each interval add another 1-2mg until you feel better.
Since you were doing roxies I'm sure 2mg of suboxone a day would be enough. You may need 4mg the first day, but after that you shouldn't need more than 2mg.