If your Flipdish POS is online and the integration to your online ordering has been setup, then anytime to receive an online order this order will successfully be received by your system and be sent to the kitchen display system or printer at the time it needs to be prepared.
You do not need to have a float session open at the time the order is received. However, if the online order is an 'unpaid' order that needs to be settled upon collection of the order, then the float session will need to be started so that your staff can find the order and take payment for that order in store.
To learn more about Flipdish's products or how to grow your online business enroll for FREE in the Flipdish Academy here: http://academy.flipdish.com/