Every project must commit to delivery on a few hard and fast dates. This is actually fortunate because it is about the only way to get out of work that is going poorly.
A Work Split provides the graceful exit by allowing one to defer the portion of work that is not understood or going poorly while saving the part that does work or will save face. A Work Split does require some advance notice since some portion of the work must still be completed before deadline.
Therefore: Project Work Group completion dates from remaining effort estimates in the Work Queue Report. Take the largest of the earliest completion dates for each work group and compare it to any hard delivery date that may apply.
The difference is your Completion Headroom. Headroom will often jitter plus or minus a day or two from week to week. But steady evaporation of headroom for any Work Group is a sure indicator for management attention. You have at your disposal reordering the Work Queue, possibly deferring whole items to later release, the Work Split already mentioned, or the public embarrassment of a Recommitment Meeting.