they have two timings like 10:00 and 12.00 in date time format how to check these time range between other two timings in c#like 10:00 and 12:30(use date time format)

Essentially you are trying to determine whether a given time range falls between a fixed time range. This sounds like homework so I'm not going to give you the full solution, but hopefully this will be enough to get you going.

You need to convert each time into a timespan - reference[^] i.e. you will end up with 4 timespan variables which I will call bottomOfRange, topOfRange, bottomOfTarget and topOfTarget

First create yourself a helper function that will compare just one timespan with the fixed range ...e.g.

bool isTimeBetween(TimeSpan InTime, TimeSpan bottomOfTarget, TimeSpan topOfTarget)
{
    // Validate the parameters
    if (bottomOfTarget> topOfTarget)
        throw new Exception("Start of range must be before end of range");

    // Check time is within the range
    if (InTime < bottomOfTarget|| InTime > topOfTarget)
        return false;
    else
        return true;
}

Then you can call that from another function that takes both of the timespans

bool isRangeInRange(TimeSpan bottomOfRange, TimeSpan topOfRange, TimeSpan bottomOfTarget, TimeSpan topOfTarget)
{
    // I've left this for you to implement
}

Then you call the second function e.g.

if (isRangeInRange(bottomOfRange, topOfRange, bottomOfTarget, topOfTarget))
    MessageBox.Show("values are in range");
else
    MessageBox.Show("values are not in range");

You've mentioned using a datetime but elsewhere are just using times, however to convert the time part of a datetime to a timespan you could use

DateTime dt1 = DateTime.Now;
bottomOfRange = new TimeSpan(dt1.Hour, dt1.Minute, dt1.Second);