Leeches will last a long time with a little maintenance. When you're ready to store them, transfer them to a much larger container. I use a large zip lock style tub about the length of a standard refrigerator shelf and 8 inches wide. Poor them into the tub and try to rinse most of the slime off. I've only rinsed them using lake water - I've never tried city water with its attendant chemicals. After rinsing, fill the tub to around half full and snap the lid in place and put the whole works into the fridge. The cold and dark of the fridge will put them into a state of hibernation. Once a week, remove the tub from the fridge and give them another rinse, remove any dead leeches and place them right back into the fridge
I've kept the same leeches up to two months using this method.
