It took us, despite some unscheduled stops - to fix a burst tire, and for a blockade by some mercenary looking, slogan shouting BJP workers - about 10 hours door to door, with the road from Delhi to Ambala being very nice, Ambala to Kalka being pretty bad (but 4 laning is in progress), and again a slow 90km hill climb from Kalka to Shimla.
Shimla was a real pleasure. It was cool and very pleasant, now sunny...
and now foggy:
and suddenly cloudy.
But overall, just very very pretty.
Highly recommended for weekend trips out of Delhi. The drive is quite enjoyable, and the climate uphill (at least in the summer) to die for!