Hi,

To send 128 bytes to the 128 bytes on-chip page buffer will take about 5 ms. (400 kHz I2C).
To write these 128 bytes to the EEPROM memory will take 5 ms.

So to write the 512 pages of a 24LC512 will take (512 * 10) = 5120 ms. (About 5 seconds).

Make sure you know where are the page boundary.
Avoid page boundary crossings! (See datasheet).

Best regards,

Luciano