A large subset of EAS radio observations by CODALEMA experiment in Nançay was used to measure the departure from a plane of the signal arrival times to the antennas. The study was done at two different scales in terms of range to the EAS axis. Below about 300m, by using a 10 antennas array triggered by neighbouring surface detectors, the average departure was found to be negligible (i.e. lower than the measurement incertitude of about 2-3 ns), leading to an equivalent "wave front curvature" radius larger than 30 km. Above the 300m range, and within the first kilometre, an extended array of several tens of self-triggered antennas was used. The measurements suggest the existence of significant time departures (of order 10 ns at 1 km range), which corresponds to an apparent curvature radius much larger than the atmosphere thickness. The main limitation of the method, in addition to the inferior time precision due to self-triggering, was the lack of accurate knowledge of corresponding EAS core locations, especially when those cores are located well outside the surface detector extent.