New tick system

This refers to WhatsApp, a messenger app on mobile phones. Whenever you send a message, a symbol appears next to it. There are four symbols: a clock when your message isn't sent (you're offline in a basement), a gray tick when it is sent (it's now on the WhatsApp server, trying to reach your correspondent who's apparently in another basement), two gray ticks when your message has been received by your friend's phone, and the two ticks turn blue when your friend opens the chat window and presumably has read the message. Many people are always on their phone when you hang out with them, but for some reason your messages turn blue only seven hours after you've sent them, and even then you never get an answer. They ignore you.

Thank you. I've never used whatsapp so I was clueless.