The time behaviour of bright spatial solitons in congruent undoped lithium niobate crystal is experimentally investigated. Full field characterization of the optical wavefront emerging from the crystal during the soliton formation process is performed by digital holographic method. Experimental results of the amplitude and phase maps of the field distribution at the exit face of the crystal allow the real-time monitoring of the evolution of the soliton beam from the application of the external field to the end of the process when the generation of the channel waveguide appears to be stable. The features of the dynamics of the soliton formation are visualized, analyzed and compared to a time-dependent numerical model.