Event code, can't sleep arduino for correct amount of time

[pylon]

@anon62290081

  for(int i = 0; i<= 6*time_interval; i++) //this is sleeping arduino for 24 seconds
  {
  LowPower.idle(SLEEP_8S, ADC_OFF, TIMER2_OFF, TIMER1_OFF, TIMER0_OFF,SPI_OFF, USART0_OFF, TWI_OFF);
  }

The comment on the first line is completely wrong. One loop run sleeps for 8 seconds (as SLEEP_8S selects), so the complete loop sleeps for 6128 = 576 seconds so about 9 and a half minutes.

Because you didn't tell us what sleeping time you actually get I guess it's that error you experienced.