It really depends on how long the process will take in your particular situation.  But if you are already in your 5th year of H-1B, it may be too late for you to do this if you are relying on being able to extend the H-1B status beyond the 6 year maximum.  Remember that PERM must be FILED before the end of your 5th year in H-1B status to be eligible to extend beyond the 6 year maximum.  In order to get the PERM filed, there has to be some prefiling recruitment done by the employer and that typically takes at least 90 days (minimum).  If you have at least that much time left, I would urge you to get the process started as soon as possible.