I am currently playing a Warlock and I am going to take the tome pact boon. I know you cannot be concentrating on two spells at once but if I am concentrating on Hex and I cast guidance immediately before an ability check (same round) would Hex end? It is six seconds or less that guidance would be up. Is that enough time for Hex to end? Could it be considered instantaneous in this case? I guess my main question is could I cast guidance immediately before a check and keep Hex active?
Hex would drop if you cast Guidance
Guidance and Hex are both concentration spells. The rules on concentration state:
Casting another spell that requires concentration
You lose concentration on a spell if you cast another spell that requires concentration. You can't concentrate on two spells at once.
There is no time limitation on this, even if it only lasts one turn you can't have concentration on both spells and hex will drop.