Starting from Delhi, a Kedarnath trip breaks into two legs that operators package very differently. The first leg - Delhi to Haridwar or Rishikesh - is the easy part: a 5-7 hour drive, an overnight Volvo bus, or a Shatabdi-class train. The second leg, Haridwar/Rishikesh onward to Sonprayag and Gaurikund, is the one that actually determines your itinerary length, typically another 10-12 hours by road through winding hill sections.
Because of that second leg's length, most Delhi-origin packages run 4-6 days rather than a quick weekend trip, and increasingly bundle a helicopter transfer from Dehradun or Sahastradhara to cut travel time dramatically - at a real premium over the road-only version. If time matters more than budget for your trip, filter for helicopter-inclusive packages specifically rather than assuming every operator offers one.