30 fps in a 60 fps timeline

Hello, I'm a beginner user of Premiere.

I have a question. I have a main video that is 60FPS, and I want to use another video as an overlay. The source of the overlay has 30FPS. My composition and the final output should be 60FPS. How does Premiere manipulate the frames of the overlay video? Are they going to be "spread" so that 1 frame of the overlay spends the same time as 2 frames of the main layer? Or, is the overlay going to be faster than its source? If 1 frame of the overlay lasts the same as 1 frame in the main 60FPS video, the overlay will be 2 times faster than its source, am I right? So, what is the case? Is there any option to choose between the two?

Thanks.

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