You have to put in accurate times in order for the TP to work for you. Otherwise it is going to put you at attractions early in the morning and then very late at night (the times with the lowest lines) and give you weird breaks throughout the day, like 2 hours in the middle of the morning and then another hour and a half at 12:30 and then another hour at 2:30.
@len even talks about that problem in an interview here.
Here is the relevant sample:
Q: What was the trickiest problem to solve during the creation of Touring Plans?
A: The concept of “free time,” where you may have 15 or 20 minutes with nothing to do before your next attraction, was a little hard to code and definitely hard to communicate to users. An example of free time is when you tell the engine you’re going to be in the Magic Kingdom for 13 hours, perhaps staying to see the nighttime fireworks, and the engine thinks it’ll only take 8 hours to see all the rides and shows you’ve selected.
If you’re busy for 8 hours in a 13-hour day, you’re going to have 5 hours of free time. The engine has to put those 5 hours of free time somewhere in the schedule. And it chooses where to place the free time so that the overall amount of time you spend waiting in line is minimized. In practice, what happens often is that the engine will put the free time in early afternoon, say between 1 pm and 4 pm, since that’s when the parks are most crowded and lines are longest. And it’ll put you on rides and in shows during the morning and evening, when lines are lowest.
Some folks will write us to say that the engine must be malfunctioning, because it has this huge chunk of free time scheduled in the middle of their day. Most folks think that the free time should come in the evening but whenever we’ve looked at the plan, it’s always optimal for the free time to come in the mid-afternoon. So we’ll encourage people to move steps around in their plan and use the ‘Evaluate’ button (which doesn’t re-arrange their steps) to see how much longer their version takes, and it’s usually a significant difference.