How long should it take for cache to render?

I am working on an effect-heavy 30-second video. I have rendered cache on User, and I selected everything to be cached. There are certain sections of my video that never seem to turn blue, no matter how long I wait. Is there a reason for this? Does it usually take more than like 30 minutes for a 2-second clip to render? I have an M4 MacBook Pro with 48 GB of RAM.