I'm using this currently in a Blueholme (Holmes Basic retroclone) campaign and it is perfect. I can't recommend this enough!

This handsomely illustrated device will allow you (the DM) to carefully track resources such as torches and lanterns, spell durations, and wandering monster rolls with simplicity. This tracker works for AD&D as well. Elegant yet powerful. I strongly recommend that you purchase this...NOW! Also pick up the Labyrinth Lord (B/X D&D) version.

This tool is simply brilliant. I have always had trouble keeping track of dungeon time (the sheets with check boxes just didn't work for me) and this handy item will do the trick. I have not decided if I am going to let the players see it in use (so that they are aware of the ticking clock) or if I will have it behind the screen. Either way, it will become an intrinsic part of my future games.

I know that this will build up the tension and unease that my adventurers feel as they ponder whether or not to stay underground a little longer, travel down one more flight of stone stairs, or peek behind one more door. With the clock ticking the minor annoyance of a lost map or water-sodden torches quickly becomes a scary problem with real consequences.

I can hardly wait!