I have a grid to display data from CDT. One of the fields is Time field. I want

What version of Appian are you on?

version 6.7

Time is not available for change in a grid unless you convert it to text, which becomes dicey when converting it back since the value entered would have to have the correct format. If you could guarentee the correct format, you could use the apply rule in conjunction with toTime(). With that said, I would highly suggest using a paging grid to display your CDT, where you select the record (CDT) that you would like to change. At the bottom of the screen create an object for entering in time with a command button to "Edit Time". Than save that change directly into the CDT and loop back to the page.

Thanks thats a start although will not be user friendly. Will try it out and see

As a side note, Grid component is not supported in mobile, so it's recommended to use the pattern that Shaun suggested using a Paging Grid. See more here for mobile support for the Appian (6.7) forms -- forum.appian.com/.../Designing_a_Mobile_Form