When do you complete training that you undertake at a guild? Is it when you complete a quest, or when you advance a level, or after a certain time, or after a certain number of experience points, etc? Thanks...

Skill training is effective immediately, role ascension only when you have completed the assigned quest.
The 'in training' message seems to be simply an artifact to explain that you cannot train again until you have levelled up.

Whie being effective immediately, the time you get the "in training" message sems to be proportinal to how much you gained, which in turn is reflected by how much money you had to pay. My priest is also the person to do ID, and getting her to level 5 took a lot of money and ages to complete, level 6 even more so both.

I think train for stats (str) is immediate. New skill (one you don't have) I got right away. Raising a level 3 to 4 in skill like sword or music, I had to rise to my next role level (bard 2 to 3) before I was trained and could take on new training. You can be training at several different guilds, once you gain membership.

yes, training takes effect immediately, and you cannot train again (currently in training) until your character rises a level as a character, not in the guild.

Okay, so if you can only train when you increase in level, would it make sense to jump around from class to class a little more often? Currently I've got a 13th level Samauri, 12th level Paladin, 12th level Ninja, 12th level Warlock, 12th level Monk, and 8th level Assassin (who was a 10th level Barbarian). Right now, these guys all raise up a level about once in a blue moon. So would it make sense for me to switch them around a bit, or should I just keep them gaining from where they are, however slowly that happens?