They get taught separately, which makes them look like three different skills. In practice they are the same decision looked at from three sides. A read tells you what range the other player is likely holding. Timing’how long they took, and at which point in the hand’tells you how comfortable they were while holding it. Sizing is how you answer: the number you put out should make sense for the hand you are representing, given what you think they hold. Change one and the other two have to move with it. That is why a bet that looks correct in isolation can still be wrong: it does not fit the rest of the story.
The most common mistake is treating a single timing tell as proof. The second is choosing a bet size from habit rather than from what you are representing. The third is reading an opponent once and then never updating, when people change gears constantly.
Reads and timing patterns vary enormously between players and are much less reliable online than in person. Sizing conventions described here are common practice rather than rules. This site only organises reference material; it does not host any game.
Pick one opponent per session and watch only their sizing. Within twenty hands you will usually see a pattern. Then start noticing how long they take before each size. Those two together are worth more than any list of tells.