When does the effect of a dominate person take hold?

[Bowincal]

A question that came up this evening concerning compulsion based spells like dominate person. Can anyone clarify when the domination takes hold of a PC once they fail their save? Is the dominated PC immediately dominated upon failing the save, and if so, when does the dominated person get to react to the caster's bidding? Is it immediate, like a summon animal spell; or does the dominated person react on his original initiative turn.

[Dolanar]

Dominate Person is handled as such (by my interpretation). Spell is cast, Person is dominated, & a command is made, on the dominated target's Next initiative count (assuming it had an initiative count to begin with) it will enact the command to the best of its ability.

[Dasrak]

Spells take effect immediately upon completion of the spell unless specifically stated otherwise. You can issue verbal commands as a free action, so there would be no further delay. The dominated creature's initiative would not change.

Note that the spell has a 1-round casting time, so the spell already takes a full round to cast and the target makes its save at the beginning of the caster's next turn.