Advance Purchase Specials

Levart - If you create an Advance Purchase special, the guest must check-in after the specified advance purchase number of days. 

e.g. advance purchase is set to 7 days and the guest checks in before then, they will not receive any discount - even if some of the stay dates cross over to after the advance purchase period.

Booking.com - The guest can check in before the advance purchase period starts, and will still receive the discount for any stay dates that are after the advance purchase period.