Various Date-related queries...

I see from the Deluge scripting help that it's possible to find out the difference between two dates in terms of milliseconds. Is the result signed, i.e. can you find out if Date1 > Date2?

I want to check if a given contract has expired, and I haven't managed to find a way to do this in Creator.

Also, is there a simple way to add a year/month/quarter/fortnight to a given date?

Contracts in my application may be paid fortnightly, monthly, quarterly, and annually.

I'd like to be able to automatically generate the expiry date from the start date, and given that 1) months have different durations, and 2) leap years exist, that is quite difficult to achieve when the only increments I can make are by days and weeks.