Hi,
I have a question about concentration spells + x rounds.
Say, you cast the spell. Concentrate a round or two on it, then cast another spell, breaking your concentration on the concentration spell.
The first spell would then last for another 2 rounds.
What if you concentrate back on the first spell? Would the 2 extra rounds refresh, or is it a fixed 2 extra rounds?
No you cannot go back and start concentrating on the spell again. Basically stopping concentration is the same as failing your concentration check while casting except the spell is already functioning. If the duration is concentration it ends immediately, if it has additional round the countdown on those start.