You can start with rishikesh, spend 2 days there camping, the best one will be pebbles resort on neelkanth route, you can take my name for discounts. there you can do river rafting the next day and visit neelkanth temple and explore city, then proceed towards mussoorie for 2 days and while returning you can explore ddn and then Haridwar while on your way back then back to Delhi. this is the best route to save time.