Does anyone know where in the core rule book it says what the cooldown for feats is, or what they are? It seems a little overpowered to just be able to use certain feats over and over, such as dodge, whenever I am attacked.
Each feat specifies when it may be used. In the case of Dodge, that is all the time.
The text of the Dodge feat says:
You gain a +1 dodge bonus to your AC. A condition that makes you lose your Dex bonus to AC also makes you lose the benefits of this feat.
So, by the text of the feat, it is applicable all the time. There is no "cool down". It may help you to stop thinking about this as an ability that you "use" and start thinking about is as a permanent increase in one of your stats (armor class).
Behind the simple rules question is your concern about this feat being overpowered. There are many reasons this is not a major concern:
- A +1 bonus to AC is not that big, except at the initial levels. Consider that a character with no special bonuses can easily have a +2 or +3 to their attack just from their Strength or Dexterity bonus.
- That small bonus is not applicable when you are denied your AC bonus.
- In order to get that small bonus, you have to spend a feat. Many people consider Dodge to be an under-powered feat. The only reason to take it is when you need it to qualify for another feat (such as Whirlwind Attack).
In general, "cool down" is a term and concept that comes from the video game world. You won't find it as a pervasive part of D&D or Pathfinder. Abilities will usually tell you exactly when, how often, and/or how many times per in-game day they can be used.
Feats are usable as often as they say they are used. There is no single rule that applies to all of them.
Some feats are entirely passive and always active. For example, the feat Leadership: if you take it, you are thereafter a leader forever and always. It doesn’t have an on or off.
Other feats are passive, but conditional. Dodge is like this. It’s a passive bonus that you receive, but only so long as you have your Dexterity bonus to AC. A condition that denies your Dexterity bonus to AC (there are many) would also turn your Dodge feat off. Without any such condition, Dodge is always there, providing you a small bonus to AC against a single enemy.
Yet other feats are passive-ish, in that they modify some other thing you were already doing. Power Attack is like this, as are all metamagic feats. These kinds of feats are passive improvements to some action you could do without the feat. In many cases, they come at a cost when used, and are therefore optional: you can choose not to use Power Attack when attacking to be more accurate, or not to use a metamagic feat on any particular spell in order to conserve higher-level spell slots.
And finally, there are feats that allow you to take new actions that weren’t available without the feat. The Vital Strike feat is an example of this, granting you a new type of attack you can use as a standard action. Without the Vital Strike feat, you could not make a vital strike attack. In that sense, Vital Strike is an “active” feat, since the feat grants you a special action, but does nothing to improve your abilities except when using that action.
Do any of these feats have a “cooldown”? Not really. They have their own rules that specify when they can be used and how they apply. Leadership is just always there; Dodge is just always there so long as you have your Dexterity bonus to AC. Vital Strike can be used every time you want to spend a standard action that way—which is usually at best once per round, but you could in theory get a bonus standard action somehow.
And then there is Power Attack, which requires you to use it before making any attacks on your turn, and then lasts until your next turn. You might think of it as a “1-round cooldown,” but it’s not really written that way. Instead, it’s written as a restriction on when it can be used (prior to making any attacks), and how long it lasts (until your next turn). Note that trying to use it repeatedly prior to making any attacks does nothing for you, as the bonuses and penalties from multiple uses would not stack (they are from the same source, the Power Attack feat).
There are cooldowns on some things in D&D 3.5 and Pathfinder. Dragon breath weapons, for example, typically cannot be used for 1d4 rounds after they have been used. Class abilities are often usable only a few times per day (this isn’t strictly a cooldown though since you usually get them back at dawn or after sleeping rather than 24 hours after you used them—but they often do have an 8-hour minimum-cooldown). The binder class from Tome of Magic has 5-round cooldowns on a number of abilities. But things that have cooldowns will state those explicitly.
As for balance, in theory feats are all balanced around being used as much as they can be. If it was important for balance that a feat not be used too often, it would have a restriction built into it to prevent that—maybe a cooldown, maybe resource usage, maybe something else—so if a feat doesn’t have such a restriction, you could rest assured that the feat was designed to be used as often as you can.
However, please bear in mind that Pathfinder is not a balanced game. Numerous feats are very good—like Leadership—and numerous feats are very bad—and that would include the Dodge feat you were concerned about. Unfortunately, recognizing the more-powerful feats and the less-powerful feats is difficult to do, as there are a lot of things that go into making a feat powerful or not, and without the context that experience brings, you are unlikely to recognize them all.
It's fairly uncommon for abilities in either Pathfinder or D&D 3.5, including those granted by feats, to have cooldowns in a manner similar to video games. Sometimes an ability will be limited to being used once per round, but that's about it; about the only exceptions are for monsters rather than PCs, such as a dragon's breath weapon. Much more common is for abilities to have daily use limits - these can be a fixed number of uses like the Paladin's Smite Evil ability, or the number of uses might depend on attribute bonuses, like the Cleric's Channel Energy. Some feats like Extra Channel can increase the daily number of uses for an ability.
Feats and other character options that have limits on how often they can be used will say so; feats that have no such limits like Dodge can be used at all times. For example, the advanced rogue talent Opportunist in Pathfinder can be used only once per round.
PC abilities in 4e are somewhat closer to having cooldowns - they're usually divided into once-per-day abilities, once-per-encounter abilities, and at-will abilities with unlimited uses.
For the most part feats don't have cooldowns. They either have trade-offs built in, like sacrificing accuracy for damage in Power Attack, or the bonuses they offer are considered small enough that the use of a feat slot is price enough, like with Dodge.
There are some feats that do have cooldowns of a sort. The Luck feats are limited to the number of luck dice you have, which are equal to the number of luck feats you have and renew daily. Many of the pisonic feats will require you to expend your pisonic focus to use, which while theoretically renewable mid-battle, effectively limits you to one such feat per battle.
But any feat that has such a limitation will explicitly say so in the description. If it doesn't, assume you can use it whenever it's applicable.