"Make good time" is an English idiom that refers to someone who is ahead of schedule with some sort of project or trip. The phrase is often used when someone is taking a road trip somewhere and has a certain amount of time scheduled for the duration. If they "make good time," it means that they will arrive at their destination well ahead of the time allotted for the whole trip. This phrase can also be used when someone is trying to do a job and is making better progress than he or she might have originally expected.
On certain occasions, people who are speaking English may look for ways to add some expressiveness and impact to their conversations with others. One good way to do this is through the use of idioms. Idioms are short phrases that may seem to mean one thing based on the literal definitions of the words they contain, but instead have unique meanings that come to be accepted in the culture in which they are used. Many idioms have to do with time and how it is managed by people, including the phrase "make good time."
Any time that this particular idiomatic expression is used, it means that someone is doing something at a fast pace. It also implies that there was a preconceived notion on behalf of the speaker about how long that it was going to take to get the thing done. The fast pace means that the person will finish ahead of schedule. As an example, someone might say, "I didn't think he'd make good time with that project, but it's done already."
The most common way that this specific phrase is used comes in association with road trips. When a person or a group of people sets out on a long journey, usually by car, they often attempt to gauge how long it will take to reach their destination. If they are reaching certain landmarks along the way faster than expected, it is often cause to use this idiom. For example, someone might say, "We should make good time if we continue to move at this pace and don't hit any traffic."
This is one idiom where the meaning has strayed far from the literal definitions of the words within it. Obviously, it would be impossible for anyone to actually make time. The figurative implication is that, by coming in ahead of schedule, some extra time is created for the person who is able to "make good time."