"However, it is possible that two miners produce a block at a similar time. This situation occurs because the acceptance of the blocks into the blockchain by the nodes of the blockchain network does not happen instantaneously.
This time lag in accepting a block may lead to another miner solving for the same exact block. But only the block with the larger size of proof of work gets accepted into the blockchain."
This is the background of how orphans are produced and handled.
Can you please explain in short
1) What is this "time lag" ? I would like to understand (detailed) what happens during this time lag, what are the full nodes exactly doing during this time until they decide to accept the block into the blockchain? Is this maybe the moment where the nodes check for all the bitocin protocol rules (refering to https://en.bitcoin.it/wiki/Protocol_rules)? Or sth else
2) What is the "size of the proof of work" exactly? Is it maybe the number of leading "zeros" in the proof of work hash, or the "nonce" number, or sth else? On which parameter must you look to know which block was the result of a more "complex work"?
3) Above mentioned protocol rules: When exactly are the nodes (or the network) checking for them, at which exact step of the bitcoin transaction/consensus cycle?: Before miners receive the transactions, after miners receive the transactions but before they start to work on the PoW hashing puzzle, or after they solved the puzzle and broadcast the block to the nodes?