Allow for time regexes to match times with precision in seconds.
Handle these times in _at_time() and adjust the according
post-processed truncate_to options within the grammar entries.Remove _time_full() and call _at_time() instead.
Conditionally truncate to units and remove unit assignments of zero.
When advancing to future time, omit checking for modified minute.
Insert and process placeholders for test entries with variable units.