Can an plan administrators' QMCSO procedures provide that a QMCSO will not be honored if the QMCSO is not submitted to the plan administrator within 31 days of the date of the order?

25 USC §1169(a)(5)(B) requires "Each group health plan shall establish reasonable procedures to determine whether medical child support orders are qualified medical child support orders and to administer the provision of benefits under such qualified orders." Nothing more definite than that regarding your issue.

I don't know that the 31 day requirement would qualify as reasonable. You might want to get a legal opinion before trying to impose that 31 day requirement. Generally, it would be better from a claims and cost management and business operations perspectives to know who you are covering and collect the premium from the employee than to have a court second guess you and order coverage you had denied.

What does 31 days have to do with whether or not a MCSO qualifies? There is nothing date sensitive about the timing of the orders, so how can the plan impose some time requirement? The plan can choose give effect to the order prospectively, so delay between the date the order is issued and the date of receipt by the plan can affect the timing of coverage, but not the application of the order.