Some do. It's more common in modules not written explicitly for D&D. Most at least have a paragraph in the introduction indicating how long it should take. IIRC, the 'Mega Modules' like the Expedition series also have a section explaining how to reduce/extend the adventure depending on the number of sessions you'd like it to last.el-remmen said:Do some modules list how long they are supposed to take? I've never seen this. . .
I've also played several of the 'Cliffhanger' and 'Original Adventures' series from the WotC site. The former are intended to be played in a series of short sessions which have clearly indicated start & end points which we've never been able to match in our games...