That would change the hash of the block header, and most likely will render the new hash invalid. From what I understand, the timestamp is included in the block header before a hash is calculated.

Back to the topic question, there seems to be no specific value for 'every few seconds'. I'm wondering if the Wiki is correct, since a miner can simply add the current timestamp, start mining, and (when a hash is found within 10 minutes) publish the block. Agree on using the timestamp as an additional source in combination with the nonce.