Currently there is no time limit on upgrading your account from a Legacy Console. In August 2016, there will just be a new step to the process (the Account Import step) that will fork your progress so that it is no longer shared between console generations. After the import process begins, the first time you log into Destiny on a current generation console (Xbox one or PS4) you will be prompted to import your progress. After you do this your progress on legacy and current generation consoles will become separated. For more information please refer to Bungie's article https://www.bungie.net/en/Help/Troubleshoot?oid=44804