Somewhere along I had it go to sleep just fine, but it didn't wake up. Now it wakes up fine, but doesn't want to go to sleep. Seems like I don't have the millis stuff right anymore, I don't get to where the comment "// HOW DO I GET HERE?" is. Too tired to see it, gonna go to bed.

#include <avr/sleep.h>

boolean leds_on = true;

unsigned long previousMillis = 0;
unsigned long currentMillis = 0;
const long interval = 1000;

ISR(INT0_vect) {
  sleep_disable();
  leds_on = true;
}

void setup() {
  // put your setup code here, to run once:
  PORTB |= (1 << PB1); // input
  DDRB &= ~(1<<PB1);

  shutdown_chip();
}

void loop() {
  
  
  if (leds_on)
  {
    cli();
    leds_on = false;
  }

  currentMillis = millis();
  if ( !(PINB & (1 << PB1)) )
  {
    charlie(3);
    
    if (currentMillis - previousMillis >= interval)
    {
      // HOW DO I GET HERE?
      charlie(5);
      delay(2000);
      shutdown_chip();
    }
    else
    {
      charlie(2);
    }
  }
  else
  {
    animate_leds();
    previousMillis = currentMillis;
  }
}

void shutdown_chip()
{
  leds_off();

  /* Clear WDRF in MCUSR */
  MCUSR &= ~(1 << WDRF);
  /* Write logical one to WDCE and WDE */
  /* Keep old prescaler setting to prevent unintentional time-out */
  WDTCR |= (1 << WDCE) | (1 << WDE);
  /* Turn off WDT */
  WDTCR = 0x00;

  ADCSRA &= ~(1 << ADEN); // turn off adc

  GIMSK |= (1 << INT0);
  GIMSK |= (1 << PCIE);

  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();
  sei(); // Enable global interrupts
  sleep_cpu();
  sleep_disable();
}

void animate_leds()
{
  for (int i = 0; i < 12; i++) {
    charlie(i);
    delay(50);
  }
  for (int i = 0; i < 12; i++) {
    charlie(11 - i);
    delay(50);
  }
}

void leds_off()
{
  DDRB &= ~(
            (1 << PB0) |
            (1 << PB2) |
            (1 << PB3) |
            (1 << PB4)
          );
  PORTB &= ~(
             (1 << PB0) |
             (1 << PB2) |
             (1 << PB3) |
             (1 << PB4)
           );
}

void charlie (int var) {
  leds_off();

  switch (var) {
    case 0: // 1
      DDRB |= (1 << PB0) | (1 << PB2); // output
      PORTB |= (1 << PB0); // HIGH
      PORTB &= ~(1 << PB2); // LOW
      break;
    case 1: // 2
      DDRB |= (1 << PB0) | (1 << PB2); // output
      PORTB |= (1 << PB2); // HIGH
      PORTB &= ~(1 << PB0); // LOW
      break;
    case 2: // 3
      DDRB |= (1 << PB2) | (1 << PB3); // output
      PORTB |= (1 << PB2); // HIGH
      PORTB &= ~(1 << PB3); // LOW
      break;
    case 3: // 4
      DDRB |= (1 << PB2) | (1 << PB3); // output
      PORTB |= (1 << PB3); // HIGH
      PORTB &= ~(1 << PB2); // LOW
      break;
    case 4: // 5
      DDRB |= (1 << PB3) | (1 << PB4); // output
      PORTB |= (1 << PB3); // HIGH
      PORTB &= ~(1 << PB4); // LOW
      break;
    case 5: // 6
      DDRB |= (1 << PB3) | (1 << PB4); // output
      PORTB |= (1 << PB4); // HIGH
      PORTB &= ~(1 << PB3); // LOW
      break;
    case 6: // 7
      DDRB |= (1 << PB0) | (1 << PB3); // output
      PORTB |= (1 << PB0); // HIGH
      PORTB &= ~(1 << PB3); // LOW
      break;
    case 7: // 8
      DDRB |= (1 << PB0) | (1 << PB3); // output
      PORTB |= (1 << PB3); // HIGH
      PORTB &= ~(1 << PB0); // LOW
      break;
    case 8: // 9
      DDRB |= (1 << PB2) | (1 << PB4); // output
      PORTB |= (1 << PB2); // HIGH
      PORTB &= ~(1 << PB4); // LOW
      break;
    case 9: // 10
      DDRB |= (1 << PB2) | (1 << PB4); // output
      PORTB |= (1 << PB4); // HIGH
      PORTB &= ~(1 << PB2); // LOW
      break;
    case 10: // 11
      DDRB |= (1 << PB0) | (1 << PB4); // output
      PORTB |= (1 << PB0); // HIGH
      PORTB &= ~(1 << PB4); // LOW
      break;
    case 11: // 12
      DDRB |= (1 << PB0) | (1 << PB4); // output
      PORTB |= (1 << PB4); // HIGH
      PORTB &= ~(1 << PB0); // LOW
      break;
    default:
      ;
  }
}