Lets see if I grok this.
You are the original poster and you make a post at 1:00 pm.
Lets say for arguments sake you get a comment made every hour on the hour after that, starting at 2.00pm
So you go back at 3:15pm and you see "you have 2 new replies".
You then go away and come back at 6.15pm and you see a message "you have 3 new replies".
Is that what you are after?