Bupe is really weird, as far as its blocking ability goes. I found that if your on maintenance at dosages of 8mg and above, it's going to take at least 72 hours to feel a strong full agonist, like heroin. If you're planning on trying to get high on codeine or hydrocodone, I would imagine you would have to wait a week or more, not only for the blockade effect to dissipate, but for your tolerance to lower as well.
I found that the maximum time I could use buprenorphine and successfully get 90% effects from a full agonist after twenty four hours was five days to a week, though when I've done this I've had to usually use a larger amount of heroin than usual.
What's really weird, is that it seems that sometimes bupe just doesn't block at all. Last year I was taking twenty four mg a day, and I met up with my friend who had some mephedrone and some really fucking good heroin. I was shooting the mephedrone for a while, thinking the dope would be a waste, but I decided to try one bag out. Surprisingly, I got really fucking high, and an incredible rush. And that was off of one bag, less than twelve hours after my last 24mg dosage of suboxone. Then I decided to go on a little bender, but after that one day, I wasn't really getting high off the heroin I was buying, which lead me to believe that the dope that I did get high off of was either really pure, or was cut with something like fentanyl or possibly dilaudid or opana (though that would seem rediculous as people would pay just as much for buying those drugs straight.)
Another time when I was taking 8mg of suboxone a day, a friend threw me a bag of dope, and again, I thought there was no way I'd get high. I sniffed the thing and again, I got completely high off of one bag.
This has happened to me several times, and it truly confuses me. 90% of the time bupe will block, but it seems every once in a while it just won't.