UPDATE 5/17: Congrats everyone, we've officially hit the 6,500,000 posts milestone today! We'll celebrate now with four consecutive days of restocks in the Shop beginning on Thursday, May 19th. Here's the updated schedule with dates and times:
[TABLE="class: grid, width: 714"]
[TR]
[TD]
Day[/TD]
[TD]
What[/TD]
[TD]
When[/TD]
[TD]
Countdown 1[/TD]
[TD]
Countdown 2[/TD]
[/TR]
[TR]
[TD]Thursday
May 19[/TD]
[TD]Cherry, Peach, Apple[/TD]
[TD]12:00PM / 8:00PM[/TD]
[TD][restocktimer]05-19T12:00:00[/restocktimer][/TD]
[TD][restocktimer]05-19T20:00:00[/restocktimer][/TD]
[/TR]
[TR]
[TD]Friday
May 20[/TD]
[TD]Start a Group, Small Mailbox, Purple Mailbox, Envelopes[/TD]
[TD]12:00PM / 8:00PM[/TD]
[TD][restocktimer]05-20T12:00:00[/restocktimer][/TD]
[TD][restocktimer]05-20T20:00:00[/restocktimer][/TD]
[/TR]
[TR]
[TD]Saturday
May 21[/TD]
[TD]Chocolate Cake, Toy Hammer[/TD]
[TD]12:00PM / 8:00PM[/TD]
[TD][restocktimer]05-21T12:00:00[/restocktimer][/TD]
[TD][restocktimer]05-21T20:00:00[/restocktimer][/TD]
[/TR]
[TR]
[TD]Sunday
May 22[/TD]
[TD]ど, う, ぶ, つ, の, 森[/TD]
[TD]12:00PM / 8:00PM[/TD]
[TD][restocktimer]05-22T12:00:00[/restocktimer][/TD]
[TD][restocktimer]05-22T20:00:00[/restocktimer][/TD]
[/TR]
[/TABLE]
All times stated are in Pacific Time. You can easily convert to Eastern Time by adding three hours or convert to BST (England) by adding eight hours. For other time zones, use the lovely 
DateAndTime.com for help, add/subtract the hours yourself by googling your time zone, or do the math using our handy countdowns!
You can expect the amount of items restocked for most items to be similar to past major restocks in TBT Directs. There will be more than what's found in minor restocks outside of large directs, but don't set your expectations beyond what past restocks have offered.
Also, given all of the countdowns and times involved in this, it's possible I've made an error somewhere. Please let me know if you notice anything that seems incorrect!