How to Parse a DateTime String to Support 24 hours timing?

I'm trying to use DateTime.TryParseExact as below:

DateTime modifiedSinceDateTime;

var succeeded = DateTime.TryParseExact(modifiedSince, "yyyy-MM-ddThh:mm:ss", 
    CultureInfo.InvariantCulture,
    DateTimeStyles.None,
    out modifiedSinceDateTime);

but it fails with this DateTime value: 2013-06-06T22:41:20 which suggests my date time pattern is not right. I think the pattern doesn't support 24 hours timing format, only up to 12 hours

What should be the correct date pattern like?