I'm not sure if there is a specific time limit when that occurs, it is just something I've noticed. I've also noticed that recently all attacks do not instantly show up in the command log or in the top left to warn you of an incoming. Sometimes they need a refresh, or there is an overall delay before you get it in your notification feed.
Example: I had 5 attacks instantly show up in my command overview at the same time, although backtracking the travel times it showed that the attacks were launched at different times. Upon landing, none of these attacks were under the effect of Helmet of Invisibility, so I'm putting the aforementioned delay as a result of the server lag. Will be interested to see if it is more response after the lag issues have been resolved.
I haven't been able to make many more observations that the ones above due to the issues with the recent update.