[Zope] Calculate difference between time input?

[Peter Arvidsson]

How do I calculate the difference between two times I get from a from?

Lets say time a = 09:45
and time b = 11:15

Then I want to calculate the difference. How do I calculate it? I'd also
like to know how to get the answers in differen formats. For example
caculating the input above I want to be able to get all of the following
results:
1:30 (One hour and thirty minutes)
1,5 (One and a half hour)
90 (Ninety minutes)

Help please :)