If we were talking about keeping properties of CT diluted to working strength in an open tray then maybe 24 hrs is about right. Often this doesn't matter as in the course of the printing session there is time to do enough prints to exhaust the developer and it is then thrown away. If the open tray were to be covered by cling film then I'd have thought it would keep longer as would be the case if it were then poured back into a bottle filled up to the top and re-used.
However I have no actual knowledge of tray developing as I use a Nova Quad tank. In that I can say from experience that CT has a very long life. Of course as each print is developed it uses some developer which has to be replaced so over the course of days or weeks depending on usage the whole Nova slot of one litre is replenished.
I haven't tried WT dev yet but I would be surprised if its keeping properties is different. I am a very low volume printer and I am still using the 1 litre container of CT which was first poured into the Nova tank in Sept 2006. In between printing sessions, days or even weeks go by with no activity and when I return to the tank, the developer is still OK.
I feel we may be doing Ilford developers a disservice here. I have been impressed with CT's longlife in a Nova tank.