There is no limit as to how far in advance you are supposed to schedule talks. I had mine done at LEAST 6 months in advance, sometimes a whole year. I was the coordinator for 2 years. That job sucks, plain and simple. Especially when you get these joker Talk Coordinators from other towns who don't know how to do their job. One of the coordinators from a nearby cong. matched the wrong dates to ALL the brothers we had scheduled from his hall. So every single week they would announce the name of the talk and the name of the speaker and every single week we would get the wrong speaker giving the wrong talk. Everyone looks at me and wonders what the heck is wrong with me and why can't I do my job. ARG!!!!!
And then, you'd inevitably get some old fart of a speaker who just throws random scriptures around with no theme or application except the typical jargon we've heard for 30 years. They didn't come that often, but if they did, I would put a little red dot next to their name in my book - in other words, NOT ACCEPTABLE - DO NOT INVITE BACK. Some talk coordinators think that if you're an elder, you should automatically go on the Outgoing list. This is not the way the Society wants it done... only those with "exceptional speaking abilities" are supposed to be giving outgoing talks. I think in some areas where there are not many excelling speakers, especially rural areas, they are a little lax with this rule in order to just have some variety of speakers.
I actually kind of liked the job, in a masochistic sort of way....