CDO

Hi everyone.
I am trying to use cdo seltimestep to sample over a file with different timesteps and over particular timesteps.
For example:
cdo -seltimestep,5,7,8,10,10,10, inputfile.nc outputfile.nc
The problem is cdo seems not to be able to select the same timestep twice and gives an error after selecting that timestep the first time. The error is shown below:
cdo seltimestep (Warning): Time step 10 not found!

Does anyone know if it is possible to select the same timestep twice and have it in the output file. Thankyou

Sylvia