This is true pretty much everywhere. The basic requirement is at least Friday or Saturday night stay, but sometimes with slight variations on that theme (like Sunday or Thursday nights being inlcuded).

In the US and the UK I have notice that if you go to book a Wed-Sat or Wed-Sun stay it will give you a split reservations with Wed and Thu nights at the higher rate and Fri and Sat nights at the much lower weekend rate. It pays to actually check Thu-Sat or Thu-Sun separately because quite often if you book that along with a separate Wed-Thu stay, you will get the Thu night at the much lower weekend rate (always IME). I have booked numerous stays throughout the US and UK this way in the past. Actually I have gotten Thu-Tue (5 nights) weekend rate stays twice at RCC in London. I haven't seen that lately though.