Composer Stephen Schwartz once counseled that to create a good musical, one must have within the first 15 minutes (at least by song three), what he called an I Want song. This would be the song that revealed the main characters goals and motivations. His point was that if you didn't clear up in the beginning what everyone was shooting for, then the audience didn't know how they were supposed to feel about what was happening on stage.
I think he had a good point. When I think about musicals I like, they tend to clear the goals and motivations deal up pretty soon. Wicked has "The Wizard and I," a clear I Want song, as the third song. Pocahontas has as its third song "Just Around the River Bend." 25th Annual Putnam County Spelling Bee tells you the goal and a bit of characterization in the title song. "Out There" in The Hunchback of Notre Dame is the second song. (I just realized that 3 out of these 4 are actually Stephen Schwartz, but I'm choosing to overlook that. I believe that other musicals follow this rule as well. I challenge you to name others.)
What does this have to do with writing? Well, I like to apply this rule to my writing as well. In The Thief Book, it picks up in the middle of a fight between the MC and her father where she states flat out the goal that will catalyze the rest of the book's action. In my old crash and burn project, I don't know when I ever got out the motivations. That might well have been one of its bigger problems.
A character's main goals and motivations need to be known up front. If you hold out too long on his or her conflict, then the readers doesn't know who they're pulling for or against of who they should care about at all. That's confusing, distracting, or worse, boring, and they'll probably put the book down.
The first key to tension and conflict is knowing who wants what and why they want it. Without that, without the I Want song, you've got nothing to go on.
How long do you feel comfortable waiting before the conflict and/ or motivations needs to be introduced?