We have analysed the first interferometric fringes recorded at Dome C, Antarctica. Measurements were done between 31/01 and 02/02/2005 at daytime. Aim of the analysis is to measure temporal fluctuations of the atmospheric piston, which are critical for interferometers and determine their sensitivity. These scales are derived through the motion of the image that is formed in the focal plane of a Fizeau interferometer. Although the coherence time of piston could not be determined directly due to insufficient temporal and spatial samplings, a lower limit was nevertheless fixed by studying the decay rate of correlation between successive fringe recordings. Coherence times are measured larger than 10 ms, i.e. at least three times higher than the median coherence time measured at the site of Paranal (3.3 ms).