Invalid expression error

Hi Team,

In my job, i have following

Script Item 1 -----> DF ------> Script Item2

Declared 3 Global variables with data type TIME.

$G_start_time,

$G_End_time

$G_Diff_time.

In the script item1 , i have written the following code :

$G_Start_time = to_char(systime(),'HH:MM:SS');

In the scirpt Item2, the following code is there.

$G_End_time = to_char(systime(),'HH:MM:SS');

$G_Diff_time = $G_End_time - $G_Start_time.;

print(' Time taken by this job is [ $G_Diff_time ] ');

When i validate the job, i am getting the following error

Please help me in this.

Regards,

Praveen.