Windows services Windows服务计时器只工作两次

我想写windows服务，它每天7点工作。但blow代码只在两天内有效。我找不到原因

蒂亚

logger.Info（“OnStart启动”）；
System.Threading.TimerCallback回调=新的System.Threading.TimerCallback（更改wpa）；
var dt=新的日期时间（DateTime.Now.Year，DateTime.Now.Month，DateTime.Now.Day，7,0,0）；
var dt2=新的日期时间（DateTime.Now.Year、DateTime.Now.Month、DateTime.Now.Day+1,0,0）；
var dt3=新的时间跨度（24,0,0）；
if（DateTime.Nowdt”）；
var timer=new System.Threading.timer（回调，null，dt3-（DateTime.Now-dt），TimeSpan.FromHours（24））；
}

  logger.Info("OnStart started");
                System.Threading.TimerCallback callback = new System.Threading.TimerCallback(change_wpa);
                var dt = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day, 7, 0, 0);
                var dt2 = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day + 1, 0, 0, 0);
                var dt3 = new TimeSpan(24, 0, 0);

                if (DateTime.Now < dt)
                {
                    logger.Info("DateTime.Now < dt");
                    var timer = new System.Threading.Timer(callback, null, dt - DateTime.Now, TimeSpan.FromHours(24));
                }
                else
                {
                    logger.Info("DateTime.Now > dt");
                    var timer = new System.Threading.Timer(callback, null, dt3 - (DateTime.Now - dt), TimeSpan.FromHours(24));
                }