  We study ionization of atoms in strong elliptically-polarized laser fields.
We focus on the physical origin of the offset angle in the photoelectron
momentum distribution and its possible relation to a specific time. By
developing a model which is based on strong-field approximation and considers
the classical Coulomb scattering, we are able to quantitatively explain recent
attoclock experiments in a wide region of laser and atomic parameters. The
offset angle can be understood as arising from the scattering of the electron
by the ionic potential when the electron exits the laser-Coulomb-formed barrier
through tunneling. The scattering time is manifested as the Coulomb-induced
ionization time lag and is encoded in the offset angle.
