If you have one day and you want to visit Dehradun then this article may help you.
How to reach : Best way to go to Dehraun is by your own car or you can also take a cab but this may be costly. One other way is taking a Volvo bus which goes from Delhi “Kashmiri gate” and “Gurgaon old bus station” if you travelling from Delhi NCR. I was travelling from Delhi. These will cost between 800-900 rs per person which is quite pocket friendly. You can leave in the night and can reach Dehradun by morning so these buses are perfect regarding your office or college timings. I have taken the bus of 8:00 pm from Gurgaon and reached Dehradun at 4:30 AM. You also have an option to choose flight from Delhi to Dehradun or from whichever city you are travelling.
A day in Dehradun :
After reaching Dehradun, you can go to the hotel and check-in as you must be tired.