As long as your existing visa/work permit is valid on the day that IRCC receives an application, the 30 days is really just a guideline. However, be absolutely sure that you are entitled to either a new work permit or an extension of the current one before you apply. If it gets returned to you as "incomplete" there will have been no "implied status" and your work would be illegal.
Ok thanks!!
One last question, I obtained my visa at the airport, so how can I extend it? Do I apply online for a new one or how do I do it? Cause I am exempt from paying the fee.