same-day shipping
Used in commercial contexts to indicate that an order will be dispatched on the same day it is received.
If you order by noon, we will ship it the same day.
This item is eligible for same-day shipping.
Similar meaning, but 即日出荷 emphasizes shipping out of the warehouse, while 当日発送 can also refer to dispatch from a store or office.
Compound of 即日 (same day) and 出荷 (shipping, forwarding).