Given, $T_0$=4 hrs, $t_0$=12 hrs
Since $t_0$ is an integral multiple of T0 ( i.e. $t_0$ = 3$T_0$ ), the desired hydrograph can be obtained by taking the sum of the ordinates of three unit hydrographs of 4-hours duration, each lagging from the other by 4-hours, and dividing the sum by 3.
A 2 hour unit hydrograph in a rather deep catchment is given below:
Compute 1 hour hydrograph for the catchment area