I don't read Gen 5:1 that way. I read it to say that in the day God made man, He made man in His image and He made man male and female.
However it's said that the ancient Hebrews taught that the Earth would exist in a fallen state for 6,000 years (1000 years corresponding to a day) and then have a rest for 1000 years.
It's thought that there were about 2000 years to the flood, 2000 years to Jesus and 2000 years till now. It's also thought that with the rebirth of Israel and other signs such as the rise of lesbianism and the rise in evolution whereby men forget the flood and creation, that we are in the last times prior to Great Tribulation. After which there will be the 1000 year reign of Christ mentioned in Revelations which would correspond to God's day of rest.
Suggest you read it again. These are the generations...in the day....
IMO it could not be more simple. We are living in the 6th day according to the Bible.
I won't be debating these matters at length here with anyone. I consider myself well schooled on the matter of eschatology, but I very much dislike the spirit of debate.
The text says what it says.