Originally Posted by NandoDave

I think I have explained to myself why there are weeknight ACWN rates - I guess this is so, if someone so chose, that they could book 3/4/5 night stays at that rate, and so long as the stay included 2 x weekend nights, the second would be free. So probably the answer to my question would be 'no - not valid, but YMMV'

Originally Posted by demue

... just book the minimum two nights on the certificate rate and the extra night(s) separately and likely cheaper. No issue to keep same room usually as long as you book same room category and of course you can email the hotel prior to your stay to link the reservations and ask to assign the same room.