As early as possible. I would say your estimates are low, especially for overseas.

Working in the catalogue business made me hyper vigilant about delays, but generally here's what I do (everything is generally sent for Christmas since that's what I grew up celebrating, so figuring for arrival by the 25th):

International cards and packages take longer, so I try to get my international list done and sent first. Sending International stuff at the first of the month often means it will get there in time. I've had international packages take months, though, and I know that their recipients usually understand about slow delivery.

Domestic packages prior to the 7th goes first class mail unless Priority is a better deal (flat rate boxes are pretty neat). After the 7th, I use Priority with delivery confirmation. It should take 2-3 days, but can take up to 5, and there's always the question of weather delays to worry about. If it is the 20th or later, I'd go with Express Mail, which is meant to be overnight, but can take 2-3 days, but does deliver on Christmas. I find the USPS to be the best financial option, but if you are worried about a valuable thing, ou might want to go with FedEx, which is more expensive, but generally more trackable. I know you have bitter experience with USPS losing valuables, so I understand if you fear using them at all. In my experience they're mostly as reliable as the rest, though. Alas, none of the services are a surefire guarantee that your stuff will arive safe and sound.

If I am ordering something from a catalogue or online, I check very carefully to see what their shipping times look like. If it is before the 4th, I will probably choose standard. On the 5th or later, I will upgrapde to the next option if it isn't dreadfully expensive. If it is after the tenth, expedited shipping is pretty much the only way to guarantee timely arrival, so I pony up.

Cards I figure will take up to a week to arrive domestically, but I know that people like to display cards as part of their decorating scheme, so I try to send as quickly as possible with the 1st of December being the earliest I will consider. Usually I do cards in fits and starts, so I have a few going out every few days up until the 18th or so. If it gets to be later than the 18th and I haven't had time, or have forgotten someone, I send Bonne Annee cards (Which means Happy New Year in French, is a very common thing in France, and can arrive any time up through the end of January and still be considered okay).

Wow, I do go on, don't I?

I agree that it's good to send stuff as soon as possible, but not so early that it appears you spent they day after Thanksgiving writing your cards. I like to wait until the first week of December.

Packages I try to send ASAP in Dec., especially if they are going overseas. You can also check with USPS (or whatever carrier you use) to find out their deadlines for guaranteed arrival by the date you want.

We were at the post office last night, 15 minutes before they closed, and it was a madhouse.

Thanks for the quick responses! I am too optimistic, it seems.

I should have mentioned that we have received the Chadwick and Northrup cards! Much thanks and holiday cheer all around.

I send all my holiday cards after Christmas. Much easier, and it gives you something to do while recovering from the chocolate binge.

I should mention that Julia's system, though effective, tends to promote extreme guilt in the recipients of said cards.