From what I can tell they simply [I]post[I] every quarter, which would be the end of March for the year. They don't expire for one year. This is from the website:
Members must respond to at least one marketing message per month for their e-Miles miles to remain active. e-Miles reserves the right to suspend a Member's e-Miles miles if such Member does not respond to at least one marketing message per month. The decision to suspend e-Miles miles will be at e-Miles discretion.
e-Miles miles are automatically submitted to Delta Air Lines for deposit into SkyMiles Bonus Miles within 30 days after the end of each calendar quarter for qualifying e-Miles increments.
e-Miles miles are deposited in 500 mile increments with overages rolling into the next quarter. e-Miles reserves the right to change the increments and/or frequency of deposits.
e-Miles miles not deposited into your SkyMiles account expire one year after the quarter in which they were earned.

Anyone read this differently?