There is no direct route for kedarnath from Rishikesh. from Rishikesh you have to take bus or car for rudraprayag/Srinagar. from there you can trek... or go upto gourikund by car and then trek upto kedarnath.
In hill now no busses at night but you can take rarely morning bus departure 4 am from rishikesh bus stand.
there is many direct bus wich can take u to the point where you can start your trek to kedarnath