We report the observation and control of ultrafast non-equilibrium many-body electron dynamics in Rydbergexcited spatially-ordered ultracold atoms created from a three-dimensional unity-filling atomic Mott insulator. By implementing time-domain Ramsey interferometry with attosecond precision in our Rydberg atomic system, we observe picosecond-scale ultrafast many-body dynamics that is essentially governed by the emergence and evolution of many-body correlations between long-range interacting atoms in an optical lattice. We analyze our observations with different theoretical approaches and find that quantum fluctuations have to be included beyond semi-classical descriptions to describe the observed dynamics. Our Rydberg lattice platform combined with an ultrafast approach, which is robust against environmental noises, opens the door for simulating stronglycorrelated electron dynamics by long-range van der Waals interaction and resonant dipole-dipole interaction to the charge-overlapping regime in synthetic ultracold atomic crystals.