So basically you need to sync to the point in unix time where the public key was generated in order to retrieve your private key for that particular address or do we get one private key per wallet (wallet.dat) because I am thinking if we do then it does not matter if the wallet is synced or not we will still be able to retrieve our private keys using the command line
You don't need to synchronize your wallet to be able to import your private key. Your private key is simply the private part of your ECDSA key pair and it is not generated based on your unix time, else collisions would be common. You can generate as many addresses as you'd like in a wallet and each address has a corresponding private key stored by your wallet.
Bitcoin Core and some other wallet uses BIP38 and the addresses are generated as children from the master key.
I was aware, its the BIP38 part that I didn't fully comprehend but now it is very well explained.