Feature flags cannot be picked after RC42

Stable branches are created 2 working days prior to the 22nd. If a
feature flag removal merge request is merged 2 working days before 
the 22nd, it will not be possible to include it in the monthly
release without delaying the whole process.

Because we deploy master changes every day, merging 3 or 4 working days
before the 22nd should be enough to get the feature in the release.

doc/development/feature_flags/process.md

@@ -88,7 +88,7 @@ Take into consideration that such action can make the feature available on
 GitLab.com shortly after the change to the feature flag is merged.
 
 Changing the default state or removing the feature flag has to be done before
-the 22nd of the month, _at least_ 2 working days before, in order for the change
+the 22nd of the month, _at least_ 3-4 working days before, in order for the change
 to be included in the final self-managed release.
 
 In addition to this, the feature behind feature flag should: