The interchannel delay in fiber-optic interferometric sensing systems affects the accuracy of demodulation, noise suppression, and signal information extraction, which can be suppressed by measuring the interchannel delay. This paper introduces calibration signals in the phase signal to measure the time delay using the phase difference between these signals. Through theoretical derivation and experimental verification, we analyzed factors affecting the accuracy of time delay measurement. The experimental results show that noise within the phase signal interferes with extracting the phase difference between calibration signals. Compared with the ellipse fitting algorithm, the single frequency signal extraction algorithm based on adaptive filtering offers a more significant stability and accuracy in phase difference measurement. It shows a good linear relationship (R² = 0.99999) for measuring the length of delayed optical fibers, with a deviation range of -0.31% to 0.22%. The precise extraction of interchannel delay supports efforts to mitigate its impact on phase signal demodulation and signal processing, broadening the application scope of sensing arrays.