Post got eaten by a grue, so the short answer: It's a free action. Necromancers have Power over Undead, which gives them the Command Undead feat, which acts like the control undead spell, which lets the caster give verbal commands to affected undead despite any language barriers.
Technically, the necromancer can even give commands when it isn't the necromancer's turn, so long as it fits within the GM-decided limit of free action speech. (See "Speak" under the Combat rules.)
My house limit is up to six seconds of speech per round, distributed across any number of free actions, is fine. Anything longer than that must wait until the next round simply because you can't cram any more speech into a six-second round--magical knowledge-imparting effects or empathy notwithstanding.
is it a free action only to undead through command undead, or is it also a free action to order a golem or animated object too?
I think he's saying it falls under the free action (say a few short lines) example in the CRB and that anything more than 6 seconds of conversation has to take place over multiple rounds since a round is 6 seconds.
So long as you're ordering them around verbally and the spell or ability itself doesn't specify an action type, you can assume a free action. There are some abilities that invve ordering around NPCs as some other action type, probably because they involve more than just talking. For this one, though, it's no different than telling your hireling or cohort to "move to flank the bugbear!".
I was always told "If it is not stated, it is a standard action."
And who or what told you that?
Friend of mine. He said the general rule for any ability is that if it is not outright stated what type of action it is, assume standard.
Well, unless he's the GM implementing his own ruling, he's wrong. (Even if he is the GM, he's still technically wrong.)
The general rule for things that aren't stated is "Ask the GM," which is really just a catch-all for rules that are unclear or vague. The GM is the one who applies his common sense and concepts to the rules (as incomplete as they are) to provide an interpretation that the player adheres to.
There are rules that actually mention that "unless otherwise stated, it's a standard action," but those rules apply to specific things, such as Magic Items, Supernatural Abilities, and so on, and really only applies when an option doesn't mention an activation method and the standard action doesn't break the intent of its function.
In this case, while the ability doesn't say it's a free action, the intent behind the ability is to verbally direct your minions to do your bidding. Not having the flexibility to direct your creatures however you want breaks the intent behind an ability that lets you do just that.