It should clearly state the length of time you have in your contract in bold type just prior to your signature on the Purchase Agreement.
For example, for our VGC purchase it states:
You may cancel this Agreement without any penalty or obligation within ten (10) calendar days of receipt of the California Time-share Plan Public Report, Multi-site Time-share Plan (Non-Specific Time-share Interest) or after the date you sign this Agreement, whichever date is later. If you decide to cancel this contract, you must notify the Seller in writing of your intent to cancel. Your notice of cancellation shall be effective upon the date sent and shall be sent to Disney Vacation Development, Inc., Attention: Membership Administration at 200 Celebration Place, Celebration, Florida 34747. Your notice of cancellation may also be sent via facsimile to 407-938-4121, or by hand delivery. Any attempt to obtain a waiver of your cancellation rights is void and of no effect. While you may execute all closing documents in advance, the closing, as evidenced by delivery of the deed or other documents before expiration of your cancellation period, is prohibited(1).
(1) The term 'notify', as used above, means that a written notice of cancellation is delivered, by any means including certified return mail receipt requested, to Disney Vacation Development, Inc., Attention: Membership Administration at 200 Celebration Place, Celebration, Florida 34747
Your specific contract and state law govern the terms.