When exchanging iMessages, looking back on the conversation sometimes the date and time is displayed above an iMessage, whilst for other iMessages there is no date and time displayed, so there isn't much vertical space between the grey message of other person I'm texting and my blue message. What is the reason for this? Is the time stamp displayed if the other person takes longer than a certain amount of time to reply? Or is it to do with whether the person starts typing immediately or leaves the message and comes back to it? I'm not sure if I explained it that well, but thanks in advance for your help. I'm just curious as to why this happens.