over 2 years ago - Gay Myers (Luzi) - Direct link
Your rating will be based on other Killers rather than the default/lowest rating. it'll adjust itself from there depending on how you play that new killer, so if you don't do so great with the new killer, you rating will be lowered. Then you'll slowly get paired with survivors you're most comfortable with.
So it depends on how you perform as a killer and then with the individual killer - if it turns out you are amazing with the new Killer from the get go, your rating will stay the same when you started the new Killer or even increase.

If you are not performing too great with the Trickster, your rating will adjust itself to how you're playing and what you're comfortable with. That will then give you the time to get the grasps of the killer and get more comfortable with him. If you are not too bad with him, but not performing like you usually do, it'll only take a few matches, however, if you truly are doing way worse with him, it might take more.

Some people are incredibly good overall with most/all killers and get the grasps of new ones they play quickly, whereas others might be really good at a few or only one, then they try someone else and might underperform. The rating then will adjust itself accordingly to those different kind of people.

Edit: To note, hours is mostly not indicative of skill and performance. There are people who have a lot of hours, but don't perform too great - maybe they know the game well, but knowing the game well does not mean you perform well in the game itself.