The same time domain structures (TDS) have been observed on two Magnetospheric Multiscale Satellites near Earth's dayside magnetopause. These TDS, traveling away from the X line along the magnetic field at 4000 km/s, accelerated field-aligned ∼5 eV electrons to ∼200 eV by a single Fermi reflection of the electrons by these overtaking barriers. Additionally, the TDS contained both positive and negative potentials, so they were a mixture of electron holes and double layers. They evolve in ∼10 km of space or 7 ms of time and their spatial scale size is 10-20 km, which is much larger than the electron gyroradius (<1 km) or the electron inertial length (4 km at the observation point, less nearer the X line).