Engineering Standard at Construction Zones:
At Construction zones, the legal requirement is that a Professional Engineer must have designed the traffic flow and signage.
Specific sign placements, frequecies and spacings are required. A diagram such as TMP-915-27 will outline same.
In that design, the distance between notice and limit is 50m/50 or 60kph, 75m for 70kph, and 100m for 80 or 90kph.
You can demand to see the Engineer's drawing, and the distance notes. If there is no warning sign, 50+ meters before the limit sign, you need to find the name of the engineer who laid this out, and file a complaint with APEGM against that person or the company doing the work, for practising without authorisation.