Thanks for the report.

One option is to simply add in the below #defines which will be automatically populated by GCC when compiling:

#define VAL_DATE __DATE__
#define VAL_TIME __TIME__ 

And can be written out to Serial for example as below:

	Serial.println(F("---------------------------------------------------"));
	Serial.println(F("Firmware Build"));
	Serial.println(F("---------------------------------------------------"));
	// Output our Validation from GCC Variables
	Serial.print(F("Date:\t"));
	Serial.println(VAL_DATE);
	Serial.print(F("Time:\t"));
	Serial.println(VAL_TIME); 

This approach, and an alternative approach using the prebuild hooks to inject any required information into your code in a Version.h file, are both explained in the below video with an example project linked:
https://www.youtube.com/watch?v=jQ8O9Hi3cDA

Note that for the ESP32 the prebuild.1 and prebuild.2 hooks are already in use, so for safety you would need to amend the board.txt file to be .7 and .8 respectively.