Delhi to Jaipur - 4 to 5hours max. distance is 250km. NH8 is fun highway to drive on, if you love driving:hap2:
don't go directly from Delhi to Mount Abu, make a stop at Jaipur. Its a nice place and there are lots of things a tourist like you might find interesting to see! plus, if you go direct it would a tiring ride for you, specially you are going via Car