I understand it takes time to include a legitimate transaction in the blockchain. And I understand to execute a SmartContract function is nothing more than sending a transaction. My question is that if it takes more time to finish a SmartContract function execution than to include a plain transaction in Blockchain.
My question is that if it takes more time to finish a SmartContract function execution than to include a plain transaction in BlockChain.
Both events - executing a smart contract function, and sending a plain transaction - both bring about state transitions. That is, they change some data in the blockchain.
At a transaction level, it may be the case that the smart contract call causes a larger state transition. In which case, technically, yes, such a transition would take physically longer to perform on a given machine's CPU/GPU. The transaction would take up more space in a block (i.e. it would cost more gas), and it would take longer for other miners to run and verify that the transition is valid.
However, at a block level, a full block is still limited to a certain size. It could be that the smart contract call is twice as complex as a plain transaction, takes twice the amount of gas, and takes twice as long to run, but the time to run and verify to contents of the whole full block is still the same.
(For reference, a full block - ~8M gas - takes in the order of 100-150 milliseconds for a miner to run and verify.)