Unsteady Analysis

Hi,
I am solving an Unsteady state problem, in which the time interval is very large, so it takes time to solve it. I interrupted the solution in between cause i saw the time step that i used to intermediate solutions is very small, so I actually want to increase the time step to save, but use the solution till this time interval(instead of solving for it again), to get the solution for the entire time interval interval.
Thanks in advance