The rules that use the category "<minute_duration-sing>" are:

<time_interval>

<digit-not_zero-pl> <time_interval_unit-hour-pl> and <minute_duration-sing> <time_interval_unit-minute-sing>

<digit-not_zero-sing> <time_interval_unit-hour-sing> and <minute_duration-sing> <time_interval_unit-minute-sing>