Event to get midnight time in C# wiforms?

There is no built in event which is fired at midnight - or any specific time, so you will have to create your own.
There are two ways to handle this:
1) Use a Timer in you app.
Set up a DateTime at class level

private runAt = DateTime.Now.AddDays(1).Date;

Create a Timer, with an interval set to 30000 - that means it will run every 30 seconds.
In the Timer.Tick event handler add:

if (DateTime.Now > runAt)
   {
   runAt = DateTime.Now.AddDays(1).Date;
   // Do your "Midnight" processing
   }

2) Set up a BackgroundWorker thread:

BackgroundWorker atMidnight = new BackgroundWorker();
atMidnight.WorkerReportsProgress = true;
atMidnight.ProgressChanged += atMidnight_ProgressChanged;
atMidnight.RunWorkerCompleted += atMidnight_RunWorkerCompleted;
atMidnight.DoWork += atMidnight_DoWork;
atMidnight.RunWorkerAsync();

And handle DoWork:

private bool terminate = false;
void atMidnight_DoWork(object sender, DoWorkEventArgs e)
    {
    BackgroundWorker worker = sender as BackgroundWorker;
    DateTime reportAt = DateTime.Now.AddDays(1).Date;
    while (!terminate)
        {
        if (DateTime.Now > reportAt)
            {
            reportAt = DateTime.Now.AddDays(1).Date;
            worker.ReportProgress(0);
            }
        Thread.Sleep(30000);
        }
    }

You can handle the ProgressChanged event and do your Midnight processing there.