Guess whos back!!!

about half an hour ago my old cat strolled in, shes had something to eat and is currently sleeping in her usual place. now i have an huge dilema.
how long do i leave it to contact her current owners so they can come and collect her?????????????????????????? its going to take ages to decide :)
for anyone whos interested please read link below including comments.
thanks, cant type much im entertaining :)

mina