Generally itinerary is only a recommendation, you are free to see anything you want, free to spend as much time as you want at each location (as long as not restricted by govt rules). However, there is a distance and time limit. You can go anywhere within the city, going outside the city may be chargeable. Also, using the cab in night (after 8 pm or before 6 am) may be chargeable unless mentioned otherwise.
In addition, it also depends on what you had finalized with the Agent. Some Agents provides Cabs at disposal basis which means cab is with you throughout the trip. However, any usage outside the pre-approved distance and time limit will attract additional charges. Many Agents gives Cabs available at Point to Point Basis, which means cab is available only for approved itinerary. Any other usage need to be informed in advance and will attract additional charges.