It could have happened to you before when you try to read some of the notification message but could not as by the time you try to read it, its disappeared from the system tray.
Here is how you can increase the time interval for which the notifications stay open before closing.
1. Open Control Panel >> Ease of Access >> Ease of Access Center >> Make it easier to focus on tasks
Now adjust the time here, for which notifications should stay open before closing.
if you want to specify a custom time in seconds, you can also do it with registry in that case refer to the source of this article.
[ Source – WindowsValley.com ]