Eight days is the unhurried Golden Triangle. Each city gets time to be seen properly, with a spare half-day in each. You can walk Old Delhi, see the Taj Mahal twice, once at sunrise and once from Mehtab Bagh across the river, and spend a day in Jaipur doing something other than monuments, such as a cooking class or a block-printing workshop.
If you want to see Pushkar, Jodhpur or Udaipur, see our 10 Days Golden Triangle with Rajasthan instead.