Zceryll's Summon Monster

[Bad Wolf]

Is there any clarification on how long the duration is?

[Extra Anchovies]

Nope. It has no stated caster level, and thus no calculable duration. Nor is there a limit on the number of active summons. You can have endless armies of summoned creatures, adding one every 5 rounds. It's a big part of what brings binders to T2 when online vestiges are available.

ETA: Apparently I am (probably) wrong. Sorry.

[Tvtyrant]

Is there any clarification on how long the duration is?

It doesn't work like a summon monster, it simply summons them. So you get them forever.

[Psyren]

I forget if this line is in ToM, but the Binder online articles provide the following:


If a supernatural ability granted by a vestige mimics the effect of a spell or shadow magic mystery (or psionic power), the caster level of that ability is always equal to a binder's effective binder level.

And even without that line, there is the more general line on RC 119 that the caster level of a creature's supernatural abilities equals its HD unless otherwise specified.

So you definitely can calculate the CL of Zceryll's summon ability.

[Cruiser1]

Is there any clarification on how long the duration is?

Summon Alien: You can summon any creature from the summon monster list that a sorcerer of your level could summon. Any creature you summon with this ability gains the pseudonatural template. Thus, at 10th level you could summon any creature from the summon monster I-V list.
The above says you are treated as a Sorcerer of your character level. Therefore when you're 10th level, your effective CL is 10, and Zceryll's summon monster ability lasts for 10 rounds.

[Chronos]

Even if that rule weren't there, no other answer really makes sense. If one insists on arguing that the RAW is infinite duration, then one ought also to argue that it needs a houserule to fix it, and the net effect is the same.