At night.
Have rehomed the bloody thing in the garage.
We haven't had a litter tray indoors for over a year. Had an outside one for a while which she didn't use so I removed it. For the last few weeks, when it's been wet outside, she has been shitting in her bed. Two mornings in a row now I've come down to it.
I don't want an indoor tray again so have locked her in the garage with tray and food where she will go every night over the winter from now on.
DC think IABU but they're not cleaning up the shit and having to do two boil washes, one for bed, one to clean machine!