I Have a table in Access as below

SI Number        Time
1.14172E+20      13:30:35
1244066650       18:58:48
1244066650       19:03:12
1244066650       19:05:50
01724656007_dsl  22:15:20
01724656007_dsl  22:18:00
01724656007_dsl  22:24:28
1141530407       10:27:49
1141530407       10:29:13

And require output in the same table is

SI Number        Time      Diff
1.14172E+20      13:30:35 
1244066650       18:58:48 
1244066650       19:03:12  0:04:24
1244066650       19:05:50  0:02:38
01724656007_dsl  22:15:20 
01724656007_dsl  22:18:00  0:02:40
01724656007_dsl  22:24:28  0:06:28
1141530407       10:27:49 
1141530407       10:29:13  0:01:24

I require as if 1st record in SI Number column is equals to 2nd record than record 2 of time column -record 1 of time column in Diff column record 2 record 1 will remain blank

Urgent help required Vijay