keymap.c

enum custom_keycodes {
  MY_CUSTOM_MACRO = SAFE_RANGE
};

//...

bool process_record_user(uint16_t keycode, keyrecord_t *record) {
  switch(keycode) {
    case MY_CUSTOM_MACRO:
      if (record->event.pressed) {
        key_timer = timer_read(); // start the timer if the event is a keydown/press
      }
      else { // read the timer and send the appropriate keycode
        if (timer_elapsed(key_timer) < TAPPING_TERM) {
          SEND_STRING(SS_LSFT(X_EQUAL)));
          return false;
        }
        else {
          SEND_STRING(SS_TAP(X_CTRL));
          return false;
        }
      }
  }
  return true;
};