When testing you might find funktions that works as expected and therefore can be passed, though you find them strange or inappropiate. I have passed a test like that.
When someone sends you a message you expect to get a popup if popups are activated in your settings and the sender also expect that you get a notification for the messages. But if you get 2 messages shortly after each other you will only receive a notification for the first message, which means that you might miss the second or won't see it until it is too late.
As the system works now this is not a bug but a feature, there is a hard coded delay between popups to stop users who get a lot of messages being bombarded with popups. As I see it a delay can not stop spam if people know about the delay, but you can prevent the spam by blocking the spammers. The delay can only be irritating for people who do not know about it..
E.g. I send a message to you to tell you that the meeting will start a half hour later than planned. While you read my message I write a new because I forgot to say that you should not pick me up on the way. You do not read message number 2 because it came after you read the first but before the delay of sending out messages.
So wouldn't it be better not to have the delay?