You can press the "increase pace"-button every ten seconds (it will be blocked before), but you don't get any additional effect for as long as the Emotion Indicator is rising. Once it stops rising, you can press the button again, if you want to. The length of time that your commands have an effect, increase with the driver's skill. In the beginning he will stay at the current pace just over 30 seconds when you press "Maintain pace", close to level 40 the effect will be almost a whole minute. Increase or decrease pace-commands or "Overtake" have a shorter effect.
If your driver is hot, that means he tries to drive faster, but he is also more error-prone. The amount of errors varies on the skill of the driver, the remaining stamina, and also on car and track. On some tracks you will need to slow him down a lot so as to avoid errors. If your driver is skidding, then you are probably running him too hot for his current skill.
I've found that in most cases it's best to run him at about 75%. That way you can get decent laptimes without too many errors. That depends on the general characteristics of our driver though.