原理其实非常简单，取出两个时间差的秒数，再在0到该秒数之间随机获取一个整数，将其做为秒添加到较小的时间上，可以说实现上并没什么技术难点，可以在数据类型的边界条件上却需要格外的注意，比如将大于 System.Int32.MaxValue 或小于 System.Int32.MinValue 的值转成 int 时，如果直接在变量前加上类型名转换（(int)d），不会有有异常产生，但得到的值却是 System.Int32.MinValue，还有就是对于Math.Abs 方法，当参数 value 等于 MinValue 将会引发 System.OverflowException 异常。

代码如下：

using System;

namespace Yyw
{
    public class DateTimeHelper
    {
        /**//// <summary>
        /// 获取随机时间
        /// <remarks>
        /// 由于Random 以当前系统时间做为种值,所以当快速运行多次该方法所得到的结果可能相同,
        /// 这时,你应该在外部初始化 Random 实例并调用 GetRandomTime(DateTime time1, DateTime time2, Random random)
        /// </remarks>
        /// </summary>
        /// <param name="time1"></param>
        /// <param name="time2"></param>
        /// <returns></returns>
        public static DateTime GetRandomTime(DateTime time1, DateTime time2)
        {
            Random random = new Random();
            return GetRandomTime(time1, time2, random);
        }

        /**//// <summary>
        /// 获取随机时间
        /// </summary>
        /// <param name="time1"></param>
        /// <param name="time2"></param>
        /// <param name="random"></param>
        /// <returns></returns>
        public static DateTime GetRandomTime(DateTime time1, DateTime time2, Random random)
        {
            DateTime minTime = new DateTime();
            DateTime maxTime = new DateTime();

            System.TimeSpan ts = new System.TimeSpan(time1.Ticks - time2.Ticks);

            // 获取两个时间相隔的秒数
            double dTotalSecontds = ts.TotalSeconds;
            int iTotalSecontds = 0;

            if (dTotalSecontds > System.Int32.MaxValue)
            {
                iTotalSecontds = System.Int32.MaxValue;
            }
            else if (dTotalSecontds < System.Int32.MinValue)
            {
                iTotalSecontds = System.Int32.MinValue;
            }
            else
            {
                iTotalSecontds = (int)dTotalSecontds;
            }

            if (iTotalSecontds > 0)
            {
                minTime = time2;
                maxTime = time1;
            }
            else if (iTotalSecontds < 0)
            {
                minTime = time1;
                maxTime = time2;
            }
            else
            {
                return time1;
            }

            int maxValue = iTotalSecontds;

            if (iTotalSecontds <= System.Int32.MinValue)
                maxValue = System.Int32.MinValue   1;

            int i = random.Next(System.Math.Abs(maxValue));

            return minTime.AddSeconds(i);
        }
    }
}
测试代码：

using System;
using NUnit.Framework;

namespace Yyw
{
    [TestFixture]
    public class DateTimeHelperFixture
    {
        /**//// <summary>
        /// 边界测试
        /// </summary>
        [Test]
        public void TestGetRandomTime()
        {
            DateTime minTime = DateTime.MinValue;
            DateTime maxTime = DateTime.MaxValue;
            Random random = new Random();

            for (int i = 0; i < 10000; i  )
            {
                DateTime randomTime = DateTimeHelper.GetRandomTime(maxTime, minTime, random);
                CheckResult(minTime, maxTime, randomTime);
            }

            for (int i = 0; i < 10000; i  )
            {
                DateTime randomTime = DateTimeHelper.GetRandomTime(minTime, maxTime, random);
                CheckResult(minTime, maxTime, randomTime);
            }
        }

        private void CheckResult(DateTime minTime, DateTime maxTime, DateTime randomTime)
        {
            System.TimeSpan ts1 = new System.TimeSpan(randomTime.Ticks - minTime.Ticks);
            System.TimeSpan ts2 = new System.TimeSpan(randomTime.Ticks - maxTime.Ticks);
            Assert.IsTrue(ts1.Seconds >= 0 && ts2.Seconds <= 0);
        }
    }
}