Api - round trip time from the order being generated in the api (clicking to submit) and api receiving an order working confirmation from the exchange.
User - same except from the time the user-handler gets the order from api to user-handler processing the working confirmation from the exchange.
Account- same except from the time the Account-handler gets the order from api to accounthandler processing the working confirmation from the exchange.
Exchange- same except from the time the exchange-handler gets the order from api to exchangehandler processing the working confirmation from the exchange.