While I don't work for the post office, I know several people who do and this is what I've been told. When mail is batched out from the PO depends upon the size of the office. Small ones, like in very small rural towns, only run one batch a day, usually around 4pm or so. Larger offices run more than once a day. Huge ones, like the main PO in Northern Virginia, that serves as a clearing PO for the NO VA and DC area, runs multiple times a day (that PO is even open for regular service like 7am-11pm on Sundays!!). Just ask your local office.....they'll be glad to let you know when mail is picked up from them.