The reductions will be effective up to late April.
Routesonline reports that Jetstar Asia will reduce services as follows:
Singapore – Darwin
01MAR20 – 14MAR20 Reduce from 5 to 4 weekly
22MAR20 – 28MAR20 Reduce from 5 to 3 weekly
19APR20 – 25APR20 Reduce from 7 to 5 weekly
https://www.routesonline.com/news/38/airlineroute/290076/jetstar-asia-febmar-2020-network-adjustment-as-of-01mar20/