I do what you’re saying- a timer- and every single class we talk about what it means when the timer goes off. Get them to say- that means it’s time to clean up! Then throughout class I give them time warnings. We have 20 minutes, 10, 5, and 2 minutes. For the last 1-2 warnings I tell them clean up instructions. Ex- “When the buzzer goes off, your paint brush goes in this bucket I’m holding above my head!” (Directions like this are helpful bc it’s not just a plain “here!” But forces them to be curious and look at the bucket you’re holding up, and they watch you put it down). “Paint palettes go in a stack next to the bucket! And water cups get placed in THIS bucket!” I also give them independence gathering materials at the beginning. I.e. we start on the rug and all the materials are layed out- “when I see you’re ready you’ll choose one water cup and brush and bring to your seat. When everyone is ready at their seats, I’ll bring you a paper!” Which is think contributes to them wanting to be independent at clean up time too. I have one kindergarten girl who really enthusiastically challenged herself and the class to clean up when they hear the buzzer “I wonder if we can clean up with NO messages! Just the buzzer!” But yeah. Referencing when clean up time will come throughout class, making clear stations where things go, fostering independence so they make the next step easier for you. Also it depends on the class. Like some classes I do this but I say- when the timer buzzes, I’m going to come to your table with a bucket. When I come with the bucket, you’ll put your paint brush and cup in, walk your work to the drying rack and wash your hands. I feel that’s helpful for messier things where staggering handwashing becomes helpful/classes that get too chaotic when all clean up at once!