Interesting - when I was booking my award trip this September, I wanted NCE-LHR-YYZ. They told me they could give me NCE-LHR on Sunday, but the LHR-YYZ leg couldn't go until the next day.

I elected to back up a day (to Saturday) and everything was booked on the same day.

If I had taken the original schedule (with the Sunday night stayover), would they have been obligated to put me up for the night? The award was in F, if that makes any difference.