Simplify some logic for doing time span operations.

git-svn-id: svn+ssh://svn.curseforge.net/wow/ovale/mainline/trunk@1113 d5049fe3-3747-40f7-a4b5-f36d6801af5f
Narrow the domains for which changing values are valid.

This is a temporary fix for ticket 306 - "and" "or" bugged.

git-svn-id: svn+ssh://svn.curseforge.net/wow/ovale/mainline/trunk@1114 d5049fe3-3747-40f7-a4b5-f36d6801af5f