I would order when you start using the bucket as you just never know. What if someone saw you doing a driveway or sidewalk rust cleaning and wanted their concrete done also and then another and before you know it, you are out and cannot make any more money because you don't have product to use to make money.
That had happened to me a while back with another product so when I start using a new container and that is the last one I have, I place an order for another as soon as I can because of the delay in getting it here because of ups.