Can you resume concentration for concentration+rounds spells?

[Gallant Armor]

I can't find a clear answer on this. For example, Minor Image has a duration of concentration + 2 rounds:

Round 1: Cast Minor Image

Round 2: Concentrate

Round 3: Do something other than concentrate, using 1 of the 2 rounds of added duration.

Round 4: Resume concentrating

Would the above example be possible?

[QuidEst]

Nope. It's concentration plus x rounds, so once you stop concentrating, it's now x rounds.