Market Order executes instantly against the best available price in the order book
DMEX is the only margin DEX that allows market orders. In effect, the market order is a Limit Order with a price slightly lower/higher than the best available price in the order book. So the Market Order is just a faster way to create a limit order with the price basically pre-filled.
When creating a MARKET order, the DMEX app will create a LIMIT order with the price +/- 1% from the best available price in the order book.
MARKET orders will execute instantly and will always pay the taker fee.
In rare cases, when a violent price move is happening the MARKET order will not execute, and instead will appear as a LIMIT order in the order list. That can happen when the price moves more than 1% while the order is being confirmed. In this case users have the option of cancelling the order and creating a new one, or waiting for the order to execute as a LIMIT order (in that case the user will only pay the maker fee).