When I calculate the sum of times i am getting 0 (Zero)

That is a text values looks like H;mm:ss format. Select the column go to,

Data | Text to columns | Finish.

Also, you have circular Reference in A31, change formula to =SUM(A1:A30)

The problem is the data, you have actually entered 00: as the first three digits, so you have entered a text string, not a time string. You can't sum text string with the SUM() function.

So, I removed the leading 0 and the values converted to time. I changed the "format" to [hh]:mm:ss so that is still displays the leading zeros. Now the SUM() will work.