how to compute percentage of time looking at corresponding values in columns

Dear all,

I am new to excel and have a doubt in a particular computation. I would highly appreciate your help in this regard.

1. Imagine 2 columns; A(having time displayed hh:mm:ss:ms format) & B (a value corresponding to time).
2. Assume only 2 possible values for column B e.g. Val1 or Val2
3. I would like to compute the percentage of time for which Val1 was in use & the same for Val2.

Any ideas how this could be done? Please suggest me some possible ways of getting this done.

Thanking you in advance,
Andy13

Added an excel sample to show the example. I hope this clears the issue little better.