As you probably know, (very) recent conversion data is lower than it will be eventually because of delays in tracking and attribution.
That's why you probably don't want to receive an alert that your conversions yesterday were 30% lower than the same day a week before, as that's likely to be a false warning. And one you'll get every day, which gets annoying.
That's why we're proposing an option to let you set a number of recent days to ignore when creating or editing your performance monitoring alerts. That way, you won't get false alerts anymore due to tracking delays.
If you'd like to give this feature request priority, please vote and/or comment on it!