The Honest Answer on a Day Trip
Delhi to Jaipur and back in a day is done constantly and it is a long day. Around 280 km each way, which is five to six hours of driving in total on a good day and considerably more if you leave late.
What that buys you is roughly five hours in Jaipur, which is Amber Fort and one or two things in the city. It is not enough for the City Palace, Jantar Mantar and Amber together at any reasonable pace.
If the day trip is what your schedule allows, take it and choose Amber Fort plus Hawa Mahal on the way back. If you have any flexibility at all, one night in Jaipur changes the trip completely, and the one-day Jaipur itinerary becomes a real day rather than a compressed one.

From Delhi: Jaipur Day Trip by Air-Conditioned Car
A top-rated Jaipur experience, bookable directly through AsiaByLocals.
From USD 100
12 hours

