We only give it 3.3V which is too low. Min is 4.5V.

If we do power from 5V, technically the 3.3V I2C bus is out of spec per the standard, but actually these chips have a V_H_MIN of only 2.2V, so it'll be fine.

To support either the MCP7940N or the DS1307, suggest DNF capacitors for the crystal (DS1307 doesn't need them, MCP7940 does), and 0 ohm links for both 3.3V and 5.0V power, so you can pick at build time which one you are loading.