The rules that use the category "<time_interval_unit-second-pl>" are:
<digit-pl> <time_interval_unit-second-pl>
<minutes-digit_sequence-pl> <time_interval_unit-second-pl>
<minutes-digit_sequence-pl> point <digit> <digit> <time_interval_unit-second-pl>
<minutes-not_digit_sequence-pl> <time_interval_unit-second-pl>
<minutes-not_digit_sequence-pl> point <digit> <digit> <time_interval_unit-second-pl>