I would imagine the second case relates to separate PNRs that are linked by calling or requesting at the gate. If you're on separate, unlinked PNRs, DL has no way of knowing that you're "companions" so you (the GM) will be upgraded at your window*, and your companion will not be upgraded at all.

If you're on linked PNRs, you will be upgraded at the companion window of 24 hours*.

If you're on the same PNR, you will be upgraded at the companion window of 24 hours*.

I have seen companion upgrades process sooner, so maybe they occasionally just upgrade folks before their window if there is very light elite demand on a particular flight and they don't foresee selling more seats.

*Assuming there is inventory available.