Any reason why you want to start your own daemon instead of just using a pool and paying the low 1% fee? I don't know how it is for XMR but with ETH or BTC if you want to mine it needs to be fully synced.

Reason why is because if you want to find the current block, you need the data from the latest block, such as the hash and merkle root, without this info its not possible to mine because your GPU wouldn't know what the winning block would be.

So in your case, you should just use a pool and pay the small fee. Or look around and maybe you can find a pool with a smaller fee than 1%. Some of those actually exist.