Which one out of the following two should be preferred while doing && operation on two values.
if (!StartTime.Equals(DateTime.MinValue) && !CreationTime.Equals(DateTime.MinValue)) Or
if (!(StartTime.Equals(DateTime.MinValue) && CreationTime.Equals(DateTime.MinValue)) What is the difference between the two?
(Not A) AND (Not B) is NOT equal to
Not (A And B) 
Personally I use the former, I find it easier to read if as much information as possible is as close to the point I need it as possible.
For instance, just now I was wondering if your question was whether it was better to put the expression on two lines or just one, until I noticed the part about the not and the parenthesis.
That is, provided they mean the same, which your expressions doesn't.
ie.
if (!a && !b) is not the same as:
if (!(a && b)) Rather:
if (!(a || b)) 
Well, it depends what you want. They both do different things, and either might be correct in the given context.
Regarding only the formatting, I prefere:
if(MyFirstExtremlyLongExpressionWhichBarelyFitsIntoALine && MySecondExtremlyLongExpressionWhichBarelyFitsIntoALine && MyThirdExtremlyLongExpressionWhichBarelyFitsIntoALine ) { // ... } But if the expressions are really long and compley, you should define temporary variables to enhance readability:
bool condition1 = MyFirstExtremlyLongExpressionWhichBarelyFitsIntoALine; bool condition2 = MySecondExtremlyLongExpressionWhichBarelyFitsIntoALine; bool condition3 = MyThirdExtremlyLongExpressionWhichBarelyFitsIntoALine; if(condition1 && condition2 && condition3) { // ... } The latter also clarifies your intention, if you are doing more complex boolean expressions:
if((!condition1 && !condition2) && condition3) { // ... } The first one is much more readable, and readability is the most important thing here.
Is the second one actually equivelent to the first statement? Shouldn't it be ||?
If you give put in the values you will see
(!1 && !1) == (0 && 0) == 0 (!1 && !0) == (0 && 1) == 0
!(1 && 1) == !1 == 0 !(1 && 0) == !0 == 1
