I didn't even know that could be an issue. I did some Googling, and it appears that how long you can leave clothes in the washer depends on local conditions, with many people reporting that they get a full day or more before it becomes a problem.

I guess I have good enough local conditions to allow for the several hours mine often sit in the washer. Maybe at some point I'll do some experiments and try to see what the limits are here, probably after I get around to building the temperature and humidity sensor network that I want to put throughout my house to better understand my HVAC system's performance.