The last seen option applies to your online status. People can see you online if you are sharing your last seen status with them. There are some conditions when you will not be seen online (the one where you are available for chats). On the other side, you can also hide your last seen status. All you need is to visit your profile- setting- privacy- account privacy- hide last seen. By doing this, your connections will not be able to see when you were online and in turn, you will also be unable to determine about them as well. MsgMee has the facility to hide your last seen if you do not want people to know about your status of availability.