Please help locate a bug related to rust-lang/time


#1
loop {
  {
    let now = time::now();
    let mut fiveam = now + Duration::hours(24);
    fiveam.tm_utcoff = now.tm_utcoff;
    fiveam.tm_hour = 5;
    fiveam.tm_min = rand::random::<i32>() % 60;
    let duration = fiveam - now;
    info!("Next backup time: {} -> {}, {} minutes to go", 
        now.ctime(), fiveam.ctime(), duration.num_minutes());
    thread::sleep_ms(duration.num_milliseconds() as u32);
  } 

  // do some daily job here
}

log of first loop:

INFO:mybackup: Next backup time: Fri Apr 10 13:25:54 2015 -> Sat Apr 11 05:37:54 2015, 972 minutes to go

log of second loop:

INFO:mybackup: Next backup time: Sat Apr 11 07:43:39 2015 -> Sat Apr 11 05:59:39 2015, -104 minutes to go

In the second loop Tm Sat Apr 11 07:43:39 2015 add 24 hours still in Apr 11. Is this a bug of rust-lang/time?

PS. I run many time, the frist loop always get a expected fiveam time.