Hi Abhishek,
If you want to skip a job on certain days, see this thread discussing preconditions:
http://scn.sap.com/message/14208049
Note that if you want the job to start at the time in the time window and NOT have the job chain wait on this job, there is a programmable way, using RedwoodSript - this feature is also available in the latest SAP BPA version 9.
The RedwoodScript job only has to submit your job, there are multiple examples in the documentation of scripts that submit a job ...
Regards,
HP