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
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.