casing olga

Hi all, My husband is a 457 visa holder and his visa will expire on December 16, 2015. His employer is still willing to sponsor him again for another 4 years on another 457. May I know when is the proper time for my husband to start the process of applying for a new 457 visa. His employer needs to re apply to be an approved Standard Business sponsor. If his previous 457 expires before a new one is approved. Can he continuously work for the company while waiting for the results of the application? I'll appreciate any advise on this.