Please write an example to each of your question (1 and 2) so that it will be easier to write an answer.
As for Time calculation, Scenario 1, If you want to add 5.50 seconds to each time in your example, you can open the Replace dialog box, and enter:
Find:
(\d\d):(\d\d)\.(\d\d)
Replace with:
\J nAdd=550; n=parseInt("\1")*6000+parseInt("\2")*100+parseInt("\3")+nAdd; s=("0000"+(n % 6000)).substr(-4); ("00"+parseInt(n/6000)).substr(-2)+":"+s.substr(0,2)+"."+s.substr(2);
and make sure the Regular Expressions option is turned on.
You can replace nAdd=550 with the actual time you want to add in 10 milliseconds.