示例一

using System;
using System.Globalization;

namespace DateTimeTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string timeStr;
            string timeFormat = "yyyy-MM-dd HH:mm:ss";

            //格式化输出DateTime对象
            timeStr = DateTime.Now.ToString(timeFormat);
            //字符串时间格式转DateTime
            DateTime dt = DateTime.ParseExact(timeStr, timeFormat, CultureInfo.CurrentCulture);

            Console.WriteLine("timeStr: {0}", timeStr);
            Console.WriteLine("dt: {0}", dt.ToString(timeFormat));

            Console.Read();
        }
    }
}

运行效果

示例：白班/夜班判断

using System;
/// <summary>
/// 关于白班与夜班时间判断
/// </summary>
public sealed class DayTimeDuty
{
	// 是否在夜班时间段
	public static bool IsNightShift()
	{
		return !IsDayShift();
	}

	// 是否在白班时间段 (8:00-20:00)
	public static bool IsDayShift()
	{
		DateTime dt = DateTime.Now;
		return (dt.Hour >= 8 && dt.Hour <= 19);
	}

	public static bool IsDayShift(DateTime dt)
	{
		return (dt.Hour >= 8 && dt.Hour <= 19);
	}

	// 是否在同班时间段
	public static bool IsSameShift(DateTime dt)
	{
		DateTime cdt = DateTime.Now;
		TimeSpan span = cdt - dt;
		//相差12小时，肯定不在同一个班次
		if (Math.Abs(span.TotalHours) >= 12)
			return false;
		return IsDayShift() == IsDayShift(dt);
	}

	// 是否在同班时间段
	public static bool IsSameShift(DateTime dt1, DateTime dt2)
	{
		TimeSpan span = dt2 - dt1;
		//相差12小时，肯定不在同一个班次
		if (Math.Abs(span.TotalHours) >= 12)
			return false;
		return IsDayShift(dt1) == IsDayShift(dt2);
	}
}