@ sandip_prince80: you may take release on 17th August (afternoon) and join on 19th August (forenoon). Being 18th as Govt. holiday, there will be no service break in this case. and i think this is the right procedure.
you can not take release on 18th August, because generally, nobody can sign on release letter on sunday. Again, taking release on 19th August forenoon is ok but joining on the same day AFTERNOON do not make sense.