  We present a study of Ioffe times in deep inelastic electron-proton
scattering. We deduce 'experimental' Ioffe-time distributions from the small-x
HERA data as described by a particular colour-dipole-model fit. We show
distributions for three representative gamma*-proton c.m. energies W and
various values of the photon virtuality Q^2. These distributions are rather
broad for transversely and very narrow for longitudinally polarised virtual
photons. The Ioffe times for W=150 GeV, for example, range from around 1000 fm
for Q^2=1 GeV^2 to around 10 fm for Q^2=100 GeV^2. Based on our results we
discuss consequences for the limitations of applicability of the dipole
picture.
