The "different clock" hombre_fatal is referring to is the "biological clock" - A single childless woman aged 35 who wants a family with two or three children has very little time to waste (assuming she wants a traditional two-biological-parent family structure which is extremely common among members of the upper middle class).

They need someone ready to make a lifetime commitment - and as it's rare to marry without dating for at least a year or so, they've only got a few rolls of the dice left.

If that's not where hombre_fatal is in his life, such women won't see a future with him.