Default Immersive mode

Is there any way to change the delay /timing of immersive mode. On every device I have, regardless of rom, I'm counting roughly four seconds from when nav keys and status bar are visible to when they hide. It seems to be independent of the three options in developer options section of settings. I looked through build.prop, but didn't see anything obvious.

This would be a handy feature for an xposed module... Who knows, maybe one already has it (I haven't found one).

Thanks

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