Under the new system where miles can be redeemed at any time, what date is used as the official posting date in Delta -- the day you actually requested the redemption of e-miles, the day it actually posted in Delta, some other date?

I currently don't have enough points to redeem for Delta miles, and I'm trying to figure out whether I should have any expectations that I will be able to use e-miles as a partner in the promo that ends 3/15.