(ABC News)–The clock is ticking on those last-minute holiday deals.

Kicking off at midnight, on what’s being called “Free Shipping Friday,” more than 900 retailers are guaranteeing delivery by Christmas Eve for free, some with surprise deals.Related:Shoppers brave snow to head to Clinton Outlets

With a record 2 billion holiday packages in the mail, there’s a good chance many will be returned, with two out of three people saying they made at least one return last year.

But not all return policies are created equal.

Costco, Kohl’s, and Bed Bath and Beyond have no time limit on most returns or exchanges, as long as you have a recepit. Others are more strict. K-Mart, Sears and Best Buy accept returns through mid to late January on most things.

Be careful with those electronics as well, as some stores may charge a hefty restocking fee.

Also, be sure to read those return policies carefully. Something as simple as opening the box could mean that you don’t get a refund.