Are you planning on going from 24 mg of buprenorphine per day to 0 mg per day? If so, factoring in 5 elimination half-lives, by the 4th day you'll have roughly 2.25 mg of buprenorphine (pre-bioavailability, 67.5 MME) left in your drug blood plasma and that will allow a little less than 75 percent free mu-opioid receptors and the ability to subjectively feel heroin with normal dosages. At day 3, you still have roughly 5.13 mg buprenorphine (153.9 MME) and that will make it more difficult to feel it without an increased dose of heroin. Math includes elimination half-life at 24 hours, many factors can affect this, but it's a rough estimate to show roughly the amount of available mu-opioid receptors and gets you in the ballpark - also, makes math significantly easier.
But, I'm a bit unclear if you were referring to how long until you can feel heroin if you completely stop your dosage, if you plan to taper (that will greatly affect the response) or if you mean when you will be able to feel heroin at 24 mg of buprenorphine per day - in that case, likely never.