At the campaign level within Facebook ads, don’t set an end date, set a daily budget. The golden rule with Facebook ads is to never turn something off that is working.
So if you set a campaign to run for seven days with a budget of $1400 to test an offer or some messaging and you discover an ad that is converting well, the temptation is to then create a new campaign with just the ad that works. The problem with this is that the Facebook algorithm will be reset and you will enter the auction system which will push your conversion costs up.
Instead, don't set an end date for the campaign, set a daily budget. Keep an eye on the campaign and switch off any ads that are not performing well every four days.
It's better to switch off all poor performing ads, or an entire poor performing campaign, than to switch off an ad that is performing well.