SCHEMA:
CREATE TABLE table_171748_3 (period VARCHAR, _percentage_trains_arriving_within_5_mins_of_scheduled_time_moving_annual_average__maa_ VARCHAR)
USER:
When was the percentage of trains arriving within 5 minutes of scheduled time 89.6%?

QUERY:
SELECT period FROM table_171748_3 WHERE _percentage_trains_arriving_within_5_mins_of_scheduled_time_moving_annual_average__maa_ = "89.6%"