Is there a limit on fulfilling orders after purchase?

[MoxieandBabs]

I've had two orders now that are gifts, and the customers contacted me saying they ordered too early, and are asking me to hold on to the orders for a week or two before shipping them. Is this a problem to just let them hang out in my open orders so I can still benefit from the Shopify shipping discounts? Or is there a time limit on fulfilling orders?