Check the connections from the DS1307 to the Arduino very carefully. I suspect that you've got a bad connection somewhere (the most likely culprits are either the SDA or SCL connections) which is eventually stressed by the heat during the day.
Pete
Check the connections from the DS1307 to the Arduino very carefully. I suspect that you've got a bad connection somewhere (the most likely culprits are either the SDA or SCL connections) which is eventually stressed by the heat during the day.
Pete