You could also use a lid if your dish comes with one. Each time you stir, you'll break up the frozen ice that has formed. Over time this creates the classic slushie texture. After doing this for about 3 hours, your slushie should be just right. You'll have enough for two large or four small slushies. Enjoy your delicious concoction.

TL;DR in Vietnamese:
Đậy kín khay bằng màng bọc thực phẩm. Đông lạnh hỗn hợp khoảng 2 tiếng, khuấy sau mỗi 30 phút. Xúc hỗn hợp slushie vào các cốc.