Jason,
the best thing to do is to set your timeline to the smaller fps rate. If you do it the other way around ( putting your 24p footage into a 60i timeline) your making FCP duplicate frames for you 24p footage.
In a 24p timeline, your 60i footage that has a lot more information, will loose the extra data that you actually don’t need.
Always scale your timeline by your smallest footage, never by your largest.
hopes this helps.
Just a very big puzzle mister man.