Planar binding states:
With this spell, you attempt to bind a celestial, an elemental, a fey, or a fiend to your service. The creature must be within range for the entire casting of the spell. […] At the completion of the casting, the target must make a Charisma saving throw. On a failed save, it is bound to serve you for the duration. If the creature was summoned or created by another spell, that spell's duration is extended to match the duration of this spell.
Most summoning spells require concentration. Would the original caster be required to continue concentrating on that spell even when planar binding extends the duration?
I was inclined to say "yes" to this, but it was pointed out that upcasting planar binding extends its duration to as much as a year and a day.
At Higher Levels. When you cast this spell using a spell slot of a higher level, the duration increases to 10 days with a 6th-level slot, to 30 days with a 7th- level slot, to 180 days with an 8th-level slot, and to a year and a day with a 9th-level spell slot.
It seems really unreasonable to expect concentration to be even over these extreme lengths of time.
Am I missing something here?
So, does planar binding require the original caster to maintain concentration on the extended summoning spell when one is present?