Group chat question

Hi there. I am currently having an issue. Everytime I join a room, I get all the messages that were sent in that room. i.e if I leave the room and join in again, I will get everything that happened before. Is there any way to only poll the ones from i.e current time. I found out that there is a setproperty method to the packets sent. Do i need to setProperty(time, system.currentmillis) then when I get it out, i use a listener and check the packet property and get the time and decide if i want to show it or not ? I find this not very efficient. Any help would be appreciated.

Thanks.

Am gonna reply to my own question since no one replied. It actually needs to be set in the admin console and set the amount of messages to that we want to display as history.