can I find out when a transaction was submitted to blockchain? Imagine transaction was sumitted at 10:00 AM. It was added to a block at 10:20. Can I find time of the transaction submission (10:00 AM) later?
I'm assuming this is just a general question, but when you submit a transaction you should receive a tx hash. You can use a site like etherscan.io to see the status of that transaction.
No, I don't think this information is stored. Although a pending transaction will show up on etherscan.io (including it seems now when it was first tracked), the submission time is not stored past the point at which the transaction is added to a block. You can only capture this information in pseudo-real time.