Time calculations in org

The following is exported from an org-mode text:

Late hours per month

It's the last day of the month, this is the time I usually leave at (based on the time I clocked in this morning)

clock in	work hours	clock out
07:30:00	8	15:30:00

However, I have saved some time from the 4 hours late allowance. Let's calculate that. Summing late hours for each day in the month

late hours
00:23:02
00:28:30
00:07:21
01:17:48
02:16:41

Finding the remaining time in hours (notice the remote table)

total allowed late hours	total late hours	remaining allowance
04:00:00	02:16:41	01:43:19

Taking the remaing from the monthly allowance:

leaving time	remaining allowance	updated leaving time
15:30:00	01:43:19	13:46:41

The following org-mode tables are used to calculate the values in the html tables below

#+NAME: leavingtime
| clock in | work hours | clock out |
|----------+------------+-----------|
| 07:30:00 |          8 |  15:30:00 |
#+TBLFM: $3=$1+$2*3600;T

#+NAME: latehours
| late hours |
|------------|
|   00:23:02 |
|   00:28:30 |
|   00:07:21 |
|   01:17:48 |
|            |
|   02:16:41 |
#+TBLFM: @>=vsum(@I..@-1);T

#+NAME: remaininghours
| total allowed late hours | total late hours | remaining allowance |
|--------------------------+------------------+---------------------|
|                 04:00:00 |         02:16:41 |            01:43:19 |
#+TBLFM: $2='(identity remote(latehours,@>$1))::$3=$1-$2;T

| leaving time | remaining allowance | updated leaving time |
|--------------+---------------------+----------------------|
|     15:30:00 |            01:43:19 |             13:46:41 |
#+TBLFM: $1='(identity remote(ltime,@2$4))::$2='(identity remote(remaininghours,@2$3))::$3=$1-$2;T