It is almost time for the gifts to be opened, but how long can you wait until you actually get them in the mail?

At this point, with only days left until Christmas, you may be too late for some deliveries, but others could still get there on time.

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Here are four things you need to know before shipping those packages this year.

1. United States Postal Service deadlines, at least for some services, have passed, but you still have options. Monday, Dec. 21 is the deadline for the post office's Priority Mail service. But it's already too late for standard and first-class mail service. If you are really procrastinating, you have until Wednesday for the Priority Mail Express service. For military mail, the deadlines for all zip codes have passed.

2. Federal Express ground and home delivery deadlines have passed, but Express Saver's deadline is Monday, Dec. 21. If you can't get to FedEx by close of business Monday, there are still option,s like FedEx 2 Day, Overnight and Same Day.

3. UPS deadlines are also looming. Friday was the deadline for 3-Day Select packages. Tuesday, you can still ship 2nd Day Air to be delivered Thursday. Wednesday you can use Next Day Air to ship in time for Christmas.

4. As for the go-to for company for quick shipping, Amazon is still offering an option for the contiguous U.S. Free shipping option for non-prime members has passed and same goes for standard shipping, but there's hope for the two day shipping with Amazon. You can shop and ship until Tuesday to get it in time for Christmas. Two day shipping is free with Amazon's Prime service.  Amazon also offers one day and same day delivery, meaning you can shop up until Dec. 24 and get it under the tree in time. The company offers free two-hour delivery for Prime members called Prime Now. If you order before 9:30 p.m. local time, you can get the gifts by midnight. That service is only available in Chicago, Los Angeles, Manhattan, Portland and San Diego from specific local stores.