Add or manage Time Interval
A Time Interval is made out of a Quantity and a Unit.
Quantity: Is a positive integer (1-n).
Unit: Simply select from one of the pre-defined values:
* Seconds * Minutes * Hours * Days * Weeks * Months * Years
For Example, the Quantity '42' and Unit 'Minutes' represents a time span of 42 minutes.
Description: A user friendly description.