As I had posted earlier in this topic, I find it rather futile to debate things "old Earth timescale" to a young Earth creationist (YEC) who denies that old Earth timescale. I would prefer arguing the point without invoking any absolute timescale.
Does either approach ever convince a YEC proponent?
And if there actually is evidence of a global flood 60+ million years ago, why wouldn't a dating denier simply suggest that you got the date wrong? In fact isn't your suggested approach impossible to use for a global flood?