Develop Reference

To pass specific Date format

How we can pass specific Date format like "MM/dd/YYYY" in place of System.DateTime in below code.
new ObjectParameter("FromDate", typeof(System.DateTime));

I'm not sure but i guess you are looking for a way to convert the DateTime to string in this format. Then you can use DateTime.ToString with an appropriate format string:
string result = DateTime.Now.ToString("MM/dd/yyyy", System.Globalization.DateTimeFormatInfo.InvariantInfo);
I'm using InvariantInfo to force the / as separator. Otherwise it would be replaced with your localized date separator. See: The "/" Custom Format Specifier.
Another way to force / as date separator is to escape the / format specifier with ':
string result = DateTime.Now.ToString("MM'/'dd'/'yyyy");

You can't.
A DateTime does not have any implicit format. It just have date and time values. Format concept only applies when you get it's textual (string) representation.
There is only two constructor of that ObjectParameter which one is expect Object and the other one expect Type as a second parameter.

You can specify how you want the DateTime formatted when using .ToString(), by entering a parameter in the ToString() method, like so: somedatetime.ToString("d");
You can read more about the formatting here: DateTime.ToString Method at MSDN

Parse DateTime in C#

I am trying to parse a TimeString that looks like:
11/Apr/2014:00:00:12 +0200
my code looks like
DateTime.ParseExact("11/Apr/2014:00:00:12 +0200", "dd/MMM/yyyy:HH:mm:ss zzz", null)
I looked at the MSDN and it looks good for me but I have no clue why I always get a FormatException.

You should add the InvariantCulture as a format provider.
var d = DateTime.ParseExact("11/Apr/2014:00:00:12 +0200", "dd/MMM/yyyy:HH:mm:ss zzz", CultureInfo.InvariantCulture);
Your format string is considering that the / and : characters are specific format separators that will resolve to the ones defined in your current culture, just as HH would signify "hours" in your format. Please refer to this page to see that the time separator and date separator are predefined and will be replaced by the culture specific values.
It is possible to escape the special characters but I think that in the long run your code will be much safer with the InvariantCulture

Is a DateTime.ToString format expression affected by the current culture locale?

I have some code that is logging a timestamp in format from a thick client app
DateTime.UtcNow.ToString("MM/dd/yy HH:mm:ss")
Now, on a client running in China (not sure exactly which locale) this is producing a date in the log with the format
11-20-13 02:14:03
I notice it's using - instead of / to delimit the parts, even though I explicitly wanted /
I tried to set the current culture to Chinese simplified zh-CN but I wasn't able to reproduce how the remote client was able to produce that string
Does current culture locale affect the output of this format string? Or does / have some other meaning I'm not aware of?

Yes, the / character is a placeholder for whatever the current culture uses to separate parts of the date. From MSDN:
The "/" custom format specifier represents the date separator, which is used to differentiate years, months, and days. The appropriate localized date separator is retrieved from the DateTimeFormatInfo.DateSeparator property of the current or specified culture.
As with other format specifiers, you can escape the / with a \:
DateTime.UtcNow.ToString(#"MM\/dd\/yy HH\:mm\:ss")
Or specify an explicit culture when formatting the string:
DateTime.UtcNow.ToString("MM/dd/yy HH:mm:ss", CultureInfo.InvariantCulture)

Yes, that's how it works. / is being replaced with the local date separator. The same applies to : as a time separator. You can find more on MSDN: Custom Date and Time Format Strings.
To change that, escape them with \:
DateTime.UtcNow.ToString(#"MM\/dd\/yy HH\:mm\:ss")

Parse Datetime string

I'm trying to convert the following string to datetime. I've searched high and low and can't find the exact formats string and I don't want to resort to parsing it manually.
var dateString = "20110828T134108+0100";
All my attempts fail with FormatException.

Have you tried this?
var date = DateTime.ParseExact( dateString
,"yyyyMMdd\THHmmsszzz"
,CultureInfo.InvariantCulture
);
From MSDN:
If format is a custom format pattern that does not include date or
time separators (such as "yyyyMMdd HHmm"), use the invariant culture
for the provider parameter and the widest form of each custom format
specifier. For example, if you want to specify hours in the format
pattern, specify the wider form, "HH", instead of the narrower form,
"H".

The documentation on the format string is here: http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx
That should get you started. :)

try this format: "yyyyMMdd'T'HHmmss"

Have you tried this:
DateTime.ParseExact("20110828T134108+0100", "yyyyMMdd'T'HHmmsszzzz", CultureInfo.InvariantCulture);

Date separator issue

I have the following code
DateTime.Now.ToString("MM/dd/yyyy")
It always gives me this output : "04.13.2011" instead of "04/13/2011". May I know why I am getting this weird issue?

You're almost certainly in a culture where that's the default date separator. If you want to force / you can quote it in the format string:
string x = DateTime.Now.ToString("MM'/'dd'/'yyyy")

Try this
DateTime.Now.ToString("MM/dd/yyyy", CultureInfo.InvariantCulture)

Use following code:
DateTime.Now.ToString("MM/dd/yyyy", System.Globalization.CultureInfo.InvariantCulture)
This ensures that the underlying date and time values do not change when the data is read or written by users from different cultures.