msgopala,
While you can stop and restart the service from a batch file, you have to do this outside of PlanetPress Workflow, as Workflow cannot restart itself if it has been stopped. You might want to use the Windows scheduled tasks to schedule the service restart. Be careful not to interrupt any jobs in the process.
The batch file commands would be two lines:
net stop "PlanetPress Watch 7"
net start "PlanetPress Watch 7"
However, I do find the problem to be a bit strange. What do you have in your process? Are you using any scripts, custom plugins? Can you give us more details about what your process is doing?
Regards,
Raphaël Lalonde Lefebvre