I'm learning from reading posts on this board that the date on the printable postage is very important because it serves as the postmark date. 

I've used the printable postage feature on a few books, and I'm sure that I've mailed packages a day or so after that date.  (I won't do that anymore.)  Luckily, so far, my post office hasn't refused to mail them. 

My question is, can I date the package for Monday but drop the package in the blue mail box on Sunday? I don't know the schedule of postal workers, but I was thinking if they check the blue mail box on Sunday before midnight, then technically my date of Monday is wrong. 

I'm probably overthinking this, but I'm just trying to head off problems and learn to navigate the PBS process.  Thanks!

Most blue boxes have the times for pickup posted on them.   No one is going to be postmarking your book late Sunday night!!  Most blue boxes don't even HAVE a Sunday pickup.

I do it all the time and I've never had any problems. I've even have some dated Saturday that were blue boxed after the last pick up and those all got to where they needed to be with no problem :)

well when using printiable postage it couldnt hurt to use the date  you know the postman will pick up your package)

this what I did when I sent a PBS package I did droped into the mailbox on a Sunday but it had a mondays date on it

(it couldnt hurt![ of course if Monday would be a hoilday (like  Nov 12) then use a Tuessday date

I do that all the time. My blue box pickup times are 7:30am and 4:00pm. So I will date alot of books with Mondays date and drop them in the box Sunday night so they go out with the first pickup. Never had any problems so far!

I think there was a discussion on this recently, maybe now documented in the Help Center.  PO is concerned if the pre-printed postage is dated much earlier than mailed, because it tends to make the transit time look longer.  They certainly don't mind if it seems to get there faster.  So it was suggested to use the expected date of mailing when you print out the postage.  Or even a day ahead if you are not sure.  That is, if you expect to put it in a box Monday, you could print the date as Tuesday, just in case of delays.  Sort of like postdating a check.