So will there be two coins immediately on 12:20 UTC time on August 1. or is there some sort of lock in period or something of that sort ?
BCC will exist once the first Bitcoin Cash block has been found. This can not be before 12:20 UTC time on August 1 but it could be hours or days later depending on how much hashing power there is.
Also how exactly do I use the Bitcoin ABC client to split the coins? I send a transaction with some flag and then another without the flag?
You just copy the wallet.dat file to your Bitcoin ABC data folder after the fork has happened and any transaction you will do will be only with your BCCs.