When estimating the maximum transmission delay Δt between adjacent nodes according to TSN (time-sensitive networking) standards, it was inevitable to introduce additional ineffective waiting time, which was referred to as “bubble delay”. The negative effect of bubble delay on increasing the end-to-end delay and decreasing the planning success rate was analyzed, and the precise measurement method of Δt was proposed for the first time based on analyzing the delay composition of Δt in fine granularity. Based on the exact Δt, the bubble delay caused by TSN planning was eliminated. A real test environment was built based on two customized TSN switching devices. The test results show that the bubble delay accounted for 26.4% of the end-to-end delay at least, and the planning success rate increased by 8.9% to 39.1% after eliminating the bubble delay.