No idea

With the French, it's always an affair

it is "five to seven" which is several things but among others a 5-7 relationship is an affair... so of those i guess Mistress?

None of them. A « cinq à sept » is when people meet after work to go have some fun, eat, drink, before heading back home.

Now, you could interpret it many ways, is it early morning (5-7 am?) Is it the mistress they go out with before heading back to the wife? Is it working overtime? Well, it's definitely not half a dozen.

Stereo Nacht : I was thinking it might be half a dozen, given that 6 falls right between the two... so maybe it's "about" a half-dozen

Gingo! : That was my thinking too, then I looked it up

aha... ze french!

We can count. Half a dozen is six, it's not 5.3 or 6.8.

From those choices it refers to mistress. Meeting your mistress after work - 5 to 7.

..and I learned something new today