mysql management - Having problem with Timestamp -

scenario: 2 tables (table1, table2) format: id:short; timestamp:short; price:single

the data in both table thesame except timestamp. timestamp given unix_time in ms.

question: minimum time difference between timestamps of same record in table1 , table2.

in theory, minimum time difference 0 or 1ms. in practice wouldn't time difference function of takes put data table along other external performance factors?

one question have tables why same record being stored in 2 places?