  The recent data for E866 experiment on the x_F dependence for charmonium
suppression in pA collisions at 800 GeV are analyzed using a time- and
energy-dependent preformed charmonium absorption cross section
\sigma_{abs}^\psi(\tau,\sqrt{s}). For \sqrt{s}=10 GeV the initially (\tau=0)
produced premeson has an absorption cross section of \sigma_{pr}~3mb. At the
same energy but for \tau -> \infty one deduces for the total cross sections
\sigma_{tot}^{J/Psi N}=(2.8\pm 0.3)mb, \sigma_{tot}^{J/Psi N}= (10.5\pm 3.6)mb.
The date are compatible with a formation time \tau_{1/2}=0.6 fm/c.
