Maths problem dividing 30 minutes into 30 seconds

It’s the hardcoded way - will work but not very flexible if you come back to this in a year and want 2 seconds

Post 12 is the proper way (with ul postfix as noted in post 14) for something that’s easy to read and maintain.

#define SECONDS_BETWEEN_PHOTOS 1 // time in seconds between two pictures
...

  delay(SECONDS_BETWEEN_PHOTOS * 1000ul); // wait for the right number of seconds

It's an Arduino function.
https://docs.arduino.cc/language-reference/en/functions/time/delay/

Just try it, you won't break anything.

Actually totally backwards. The use of constants to convert human terms like minutes or seconds to computer terms like milli-seconds is the self documenting way to write code. But hey, I only have 65 years experience so ......