Matthew 17:1 and Mark 9:2 both talk about ‘after six days’, but why does Luke 9:28 say ‘after about eight days’? What is the significance?

This text is from a transcript of a talk by David Gooding, entitled ‘Key New Testament Themes’ (1996).

That could be little more than the difference between the Greek and Hebrew way of counting time. Just as we have set periods, when we say, 'about ten days', what we mean is just a little bit more than a week. So it could be nothing more than that. If you want to see theological significance in it, you could say after six days, in the Jewish thinking, comes a seventh, which is a Sabbath. On the other hand, 'about eight days afterwards' can be theologically significant. It was in certain of the ritual sacrifices in Old Testament. Some courses were for seven days plus an eighth day, so that the eighth day was a kind of new beginning. So folks that want to see, or think there is, some theological significance in the difference would suggest that it's more than just a linguistic difference. This is the new kingdom, the eighth day. But I'd imagine when Luke says it's about eight days, he's using the Greek way of talking, rather than straight Hebrew.