While Market orders are executed as quickly as possible (usually within seconds), there are a few things to keep in mind that may cause certain delays.
The market is closed
If you place an order outside of a market's trading hours, your trade will only be executed once the market opens again.
Low liquidity
When demand greatly exceeds supply, or vice versa, a delay in the execution of your trade may occur.
Trading venue type
Some markets, such as Over-The-Counter markets and LSE AIM for example, are known for their illiquidity especially when compared with other popular trading venues like NYSE and NASDAQ. The same may be said to apply to orders raised on the Malta Stock Exchange, albeit to a differing degree.
In such cases, execution delays may be expected.