The Shipvine Terms and Conditions state that the same-day shipping guarantee for low-volume fulfillment requests (orders) submitted by noon Eastern is suspended if you send us more than 4 times your daily average order volume. If you send more than this amount, then the system will start backing out the Ship By date on newly-received fulfillment requests until the queue of open fulfillment requests for your merchant account starts getting under control.

In other words, Shipvine will try to ship all of your orders as quickly as possible (we're not backing out the Start Ship date on the fulfillment request), but we simply can't guarantee it during high-traffic spikes, especially if multiple merchants are spiking at the same time. 

During the month of December, Shipvine increases the allowed multiplier to 5 times instead of 4 times your daily average order volume. Additionally, for new merchants or for small merchants, a floor of 25 fulfillment requests is provided.