Can you travel from Delhi to Manali in one day by car or bus?

I would say yes you can travel from Delhi to Manali in one day by car or bus as the travel time from Delhi to Manali is around 12–16 hrs.

If you travel by car from Delhi to Manali you might reach early and might take around 12–14 hrs. But if you travel by Bus from Delhi to Manali, it might take around 12–16 hrs to reach.

Also you can travel from Delhi to Manali by Volvo Bus and the timings are from 4PM – 11 PM, only overnight journey can be done by Volvo Bus.