laterthan fix and acceptance tests

Current state makes it useless.

Redmine: https://dev.cfengine.com/issues/6530

Please backport to 3.6.x for inclusion in 3.6.2.
Narrowing the ranges of everything but year removes a valuable feature.
You have not exhibited the policy code I challenged you to exhibit, that performs the necessary arithmetic to turn the start date-and-time of a process into the correct laterthan invocation for a time some definite number of minutes later.  I contend that
* This was trivial with the previous ranges, just add the required number to the minutes field;
* This is now so hard as to be functionally impossible with laterthan().

I see no argument other than "it looks odd to me" for this featurectomy, so I am violently opposed to it.