You can see transactions on https://optimistic.etherscan.io/ as soon as the sequencer accepts them. If a transaction has not been posted to L1 yet, it will be shown with the transaction index and Confirmed by Sequencer.
After a transaction is published to L1, the transaction publication details are added and you can see not just the transaction's index, but also a link to the block where it is published, how many blocks have passed since then (the more there were, the less chance of a chain reorg that would remove the block):
After the state root is also published to L1, those details are also available on Etherscan:
