  We have studied the dependence of the allowed space of the atmospheric
neutrino oscillation parameters on the time of exposure for a magnetized Iron
CALorimeter (ICAL) detector at the India-based Neutrino Observatory (INO). We
have performed a Monte Carlo simulation for a 50 kTon ICAL detector generating
events by the neutrino generator NUANCE and simulating the detector response by
GEANT. A chi-square analysis for the ratio of the up-going and down-going
neutrinos as a function of $L/E$ is performed and the allowed regions at 90%
and 99% CL are displayed. These results are found to be better than the current
experimental results of MINOS and Super-K. The possibilities of further
improvement have also been discussed.
