Training in the Span

The Beginning Career

Characters under 5th level do not need to train to level up. During the beginning of their career, they are studying during their downtime, and that is enough to advance their level. During this time, when a new level is hit, a character instantly gains their new hit point max, base attack bonus, and saves. After being able to sleep for 8 hours, they gain their skills and other benefits of their new level.

Higher Levels

When the character reaches 5th level and beyond, they must train to achieve their next level. Upon reaching enough XP to get to the next level they can start their training. It takes a number of days indicated on the table below of non-consecutive training days to gain the benefits of the new level.
During this time, a character can still gain XP since the days do not have to be consecutive. But, a character cannot gain another level until they train for their previous level. In such cases, a charcter is always 1 experience point from gaining the next level.

What is Training

When a character starts their training, they must do it in a location that aligns with the class level they are gaining. A fighter trains in the military ward, a cleric in the church, a bard in the school, and so on. Sorcerers spend this time in reflection, trying to unlock the secrets of their heritage.
You are considered to be training for 8 hours in a day. Anything that interrupts your training causes it to pause, and you must make up those hours in the same day. Failure to do so means you lost that days worth of training, and must start over again on another day. Once your eight hours are complete, you may go about your day in any way you wish. But, training is very draining to the mind and body. Any task beyond socializing and basic things, ie combat, you are considered fatigued. 

Level	Days
1	0
5	2
8	4
9	6
13	8
15	12
17	15

Retraining

Sometimes a player may regret certain choices they have made during their career and wish to retrain those choices. A rogue that wished they had taken a different class option, a fighter wishing to swap a feat for another now they aren't dual wielding, or just wanting to move skill points around.
When a character can make time for retraining they must visit a teacher. This teacher must be the same class and at least high enough level that the option can be taken. So, if a rogue is wishing to switch out their 10th level Special ability, they must find a rogue of at least 10th level to help in the task.
See the Players Handbook II for more information.

Retraining Option	Time	GPCost
Class feature	1 week/2 levels1	500 gp/week
Feat	2 weeks	50 gp
Skill	1 week2	25 gp2
Spell	1 day	5 gp/spell level
Substitution level3	1 week/2 levels1	500 gp/week

1 Based on the original level at which the class feature or sub- stitution level is gained.
2 Per skill rank changed.
3 Substitution levels are located in the Planar Handbook