When exiting a trade, you can do so under four different assumptions. In the best of worlds, exit technique number one is the profit target.   Exit technique number two is the trailing stop, which comes into play when the market is starting to move against you after you have accumulated an open profit. Number three is the stop loss for the occurrences when the trade goes against you right off the bat. Finally, you also can exit with a time-based stop, possibly in combination with any of exit techniques one to three. The time based stop is setting a time like at end of the day or when you leave for work etc.
Just a note:
A “margin call†in not an exit strategy.