Your VI is a bit of a mess (e.g. why is the diagram and front panel maximized to the screen? Why is there a greedy while loop without wait burning all CPU doing nothing useful? The result never changes because the input is a constant! No loop needed.)
In any case, you are combining the time and date string without space between the parts, so you probably want to specify exactly how the parts are arranged. The following will give your desired result:
I need while loop because I am gonna use a time stamp, the current one and then followed by generating a geometric sequence using shift register.At this point, I c no use of while loop which makes things crazy from u r perspective.