Need help with laundry machine etiquette in an apartment

Just wanted to get some opinions - there's only one washer and dryer in this particular building (12 suites) and I've been waiting about 20 minutes... somebody has left their wet clothes in the washer and has a basket of laundry next to the washer (presumably to stake their position in line). How long do you think is it appropriate to wait before I just take these clothes out and put in my own? We all have laundry to do!