It will take max 5-10 mins from ISBT as there are only 3 stations in between, and from where will u be coming to ISBT ... coz ISBT to Rajiv Chowk is on Underground Track ... so if u will be coming from the Overhead Track..than u have to switch to the underground one. If u r coming to ISBT by other means (like bus etc) then u have to pick only one 1 train from the underground track to Rajiv chowk (Rajiv Chowk is the name of the CP station.)
If u say .. then i can meet u at ISBT itself coz i will be coming from the Elevated Line and will change to the underground line at ISBT.