Maybe not !
A plan once approved is valid for a start within 1 year of the date of approval.
Still all good ? Probably, but, did you advise the building inspector when you started ?
The only way that council know that work has commenced is if you notified the building inspector. It's in the letter of approval that comes with the stamped plan, along with the building inspector notice forms.
If you do not notify the building inspector, it is possible that after 1 year the plan will lapse. Bingo. All of a sudden your building work is unauthorised.
Look, the BI's generally are reasonable people, and would probably try and get hold of you by phone to ask if this work was done, but if they can't get hold of you for whatever reason, the plan can lapse.
UPDATE - with the miracles of the city of cape towns electronic plans management system, it is now likely that your plan will " lapsed ": after the 12 month period BY THEIR COMPUTER, and not your friendly BI.
Doesn't matter what the work proposed is, the BI may not even come out to inspect your little covered patio, but he needs to be notified so he can close the file.
NB, you should also notify him on completion and ask for an " occupancy certificate"
Occupancy certificate is just their document description, applies equally to a new house or a little boundary wall.
Last thing is - if it has a roof, any excavation, or a foundation, it requires a plan. Your louvre awning is a roof. A swimming pool has lots of rules and needs an approved plan. Your little thatched gazebo - fire regulations. Boundary walls, - the City has a walling policy that needs to be complied with.
Get the plan drawn and approved before starting work, and call the Building Inspector when you do.
Due to the wonders of the interweb, these posts crop up all over the world, be aware that we practice in the City of Cape Town in South Africa, and the information shared relates to out experience of the local requirements. Wherever in the world you are, check with your local authority, or a locally experienced architectural professional.