Lancastrian...I think thats an everyday issue even before you take the security aspect in! LOL!
At my airline the seatbelt sign is switched on 20 mins before landing...but thats an "expected" 20 mins, it could be a lot longer once you take into account holding patterns, taxi times etc...it could be anything from 20mins to 2 hours! LOL!
I remember not so long ago flying back from India with a passenger who clearly picked some gastro problem through dodgy food. The guy was mortified to whole flight but also incredibly ill! We blocked a loo just for his use which he spent most of the flight in. Then after everyone was all bucked up (including the crew) the poor lad ran past me and straight into the loo for more! What did I do?? Well not much...I rang the CSD who then rang the captain who basically said we were to land anyway. All I could do was talk through the toilet door and tell him to hold on for landing and not come out until we were off the runway!
Sometimes unusual things happen and we need to make the rules work for them!