external VCTCXO Clipped Sine Wave Oscillator RTC

[doanerock]

I am designing a clock using the esp32. I am looking to attache an external Oscillator in order to increase the accuracy of the esp32's RTC.

I am not looking to use deep sleep at all. I am looking to have the ESP32 running a display at all times and taking readings in from a couple of sensors like temperature and humidity via i2c. I am looking at using an Oscillator that offers±1ppm. With a ±1ppm VCTCXO Oscillator I should be able to not the clock by more than 53 seconds in a year.

Is a 40MHz VCTCXO Clipped Sine Wave Oscillator the best to use or would a different type of Oscillator/frequency be better?
So I should be connecting the Oscillator to XTL_CLK (also known as CPU_CLK) pin?

Is this correct or did I miss something.