"Summon" universal monster rule – how long will they stay

[Natural 1s]

How long will stay monster which was summoned by another summoned monster?

For example: I will summon Babau#1 and he will successfully use his Summon (Sp) ability to summon his Babau#2 friend.

Will Babau#2 stay
1) 3 rounds – because Babau#1's ability

Summon (Sp) wrote:

1/day—summon (level 3, 1 babau at 40%)

2) untill Babau#1 stays summoned

3) 7 rounds – because Babau1 has caster level 7

4) 1 hour – because

Universal Monster Rules for Summon (Sp) wrote:

Summoned creatures automatically return whence they came after 1 hour.

[bbangerter]

Zero rounds.

Summoned creatures cannot use their summon abilities to summon additional creatures.

SRD wrote:

A summoned monster cannot summon or otherwise conjure another creature, nor can it use any teleportation or planar travel abilities.

[Natural 1s]

Thank you.