To confirm your booking on a tour, a non-refundable deposit of 25% of the tour cost is needed. For most parks and tours, If you are booking more than 5 months in advance you only need to pay the deposit. The final balance can be paid 4 months in advance.
For Ranthambore the permits are booked 12 months in advance. You need to pay the deposit + 25% additional for permits. If you are booking the tour much in advance then you can pay the deposit and pay the 25% additional for the permits atleast 13 months in advance.