What's the latest that I can ship something I sold on ebay?

So ebay recommends that I ship my item (an iphone) within 24 hours, but the post office isn't open until three more days, is it okay for me to ship it then instead? Please help.

Added (1). Thanks for all the advice guys! And I actually did contact the seller this morning but he hasn't answered, oh well…

I wouldn't recommend it, the Hutts don't take kindly to delays in shipments
Just ask Han Solo.

Yes, that's OK. To be a good seller, use my eBay on ebay.com to send a message to the buyer, and tell them that now. That way they won't wonder what's going on, and they might give you better feedback.

P.S. It *is* often possible to ship even when the post office is closed. For instance, the post office near me has a machine that's available 24/7 where I can ship stuff any time.

As a fellow eBayer I'd say you should contact your Buyer right away and tell them that you will ship when the post office reopens (in case they are from another country, let them know that there's a holiday tomorrow hence the post office is closed).
You can also print out your postage with the eBay tool for shipping and that will "count" as shipping your item (it will show as the item being ready for shipment and thus not count "against" you for shipping when the post office reopens--but even if you do this, let your Buyer know about the delay).
Hope this helps!

You should put that in your advertisement as a condition of sale, not after the fact.

If you must delay, communicate early and often with the purchaser to ensure it is OK with them.

Don't take offense if you are down graded for not shipping promptly.

You might be able to make up for shipping late by doing a free overnight shipment, but that expense will be all on you and will eat up any profits.

Since the PO isn't open, make sure you acknowledge to your customer about the shipping, and tell them it will be shipped as soon as possible. You could package it and print postage online, then make it ready to ship as soon as the PO is open. A tracking number will be available as soon as you print the postage.