Calculating selective data

Hello All,

I have a work report that I need to do but I cannot finish it so I'll be grateful if you help me do it.
My issue is the following - there are two types of scripts (A & B) happening randomly.
The data I get is whether it's script A or B and a time stamp. I need to calculate the time one of the scripts (no matter which of them) happened after the other (and not after the same one) and to sum it for a particular period.
For example:

1. A - 12:25:30
2. A - 12:36:45
3. B - 12:38:12
4. A - 12:40:51
5. B - 12:41:24
6. B - 12:43:02
7. B - 12:45:15
8. A - 12:47:00
9. B - 12:48:12

I need the times for scripts A & B separately:
A - I need the sum of the time 4 happened after 3 and 8 - after 7
B - 3 after 2, 5 after 4 and 9 after 8.

I am really sorry that I cannot explain it better.
Thank you in advance!