When reporting revenue for a given month in sales orders (all work or services performed during same month )
The sales orders are in customers possession waiting on approval.
Our company can't invoice without a signed sales order. If you accrue all revenue during that month even though you won't invoice until the following month, is there an absolute time frame when invoicing must be turned in the following month?

Accrual accounting means you are matching revenues and expenses for a particular time thus the revenue must be bought to account when performed (completed) any time limit is associated with your internal procedures and bad debt policy. It would seem that your proceedures aren't properly framed if work could be performed without the order being to hand. If you accept verbal orders then you should be able to invoice