We take pre-orders when we run out of stock. On the product page, we provide a tentative timeline when the product is expected to be back in stock. Please note that the timeline provided is "tentative", as it can be impacted by many factors (e.g. delay at manufacturer's end, customs taking more time than expected etc.), but we try to provide our best guess based on the past experience.
We never take any pre-orders unless we have already placed the order with manufacturer for sufficient number of units.
As soon as we receive the products after customs clearance, we start shipping them.