My answer would be when you're retired!
I realise that nine to five, Monday to Friday jobs are probably in the minority now, with flexible working hours, and varying shift patterns - not to mention the fact that we all want shops, and services to be available 24-7, but I miss my weekends!
I was forced into early retirement due to ill health - very reluctantly, I loved my job and wanted to keep working. I have to say that one of the things I miss most about working (apart from a higher income and a social life) is that Friday feeling!
My days are often dictated by my pain levels, so I can't even give myself a faux weekend by getting chores done midweek and relaxing on Saturday and Sunday - often I'm forced to rest and let housework and chores build up through the week, and then do them when I feel able - whatever day that might be.
I know early retirement probably sounds wonderful to a lot of people - especially those who are unfortunate enough to be doing a job they aren't passionate about, but believe me, there are plenty of downsides. The next time you're struggling through your Wednesday hump day, take a moment to be thankful for your weekend - it will come eventually, I promise!