time signature for variable time steps

Hi. I am outputing vtk file with variable time steps. However the file series are named like data_parav_000n.vtk, where n is the time steps. However for a variable time stepping n does not corresponds to the physical time. I am outputing vtk file as rectiliniar grid and the header looks like the following

# vtk DataFile Version 3.0data_parav
BINARY
DATASET RECTILINEAR_GRID
DIMENSIONS    1  257 1153

X_COORDINATES     1 float
#### (number)
Y_COORDINATES   257 float
#############(257 numbers)
SCALAR Temp_d float 1
LOOKUP_TABLE default
###########

and other scalar parameters

How do I add actual physical time in the paraview time series?