Your order will go through when there are enough shares available at the specified price or number. Keep in mind that there must be a buyer and seller on both sides of the trade for an order to execute. Also, the orders are executed based on the price/time priority. If there are other orders placed before your order at the same price, those orders will be given priority by the exchange, and they will be executed first.

In case you have placed an AMO order, it will be executed after market opens. An SL and an SLM order can only get executed once the trigger price is hit.