It sounds like you are a confused a little bit.
Firstly, 820 is the onshore application and 309 is the offshore. For a 820 you must be onshore when granted and a 309 offshore when it is granted.
The is great you have been approved for a second working holiday visa that will give you time to gather alot of evidence
. You can submit your 820 before the second working holiday visa expires. Once you submit the 820 you will be granted a bridging visa A (BVA) which comes into effect when the WHV expires. While the BVA is in effect it allows you to stay in Australia and work while you wait for a decision. It does not allow you to travel out of Australia so if you want to travel overseas you need to apply for a BVB.
If you have any questions please feel free to ask