Wake turbulence categories are based on worst case wake with worst case stability of the wake vortex so are extended to extreme periods for 'safety'. Have the airport(s) invest in a LIDAR system that will monitor actual wake turbulence such as WindTracer by LM. (I am not related to the company but have seen it work)
Lockheed Martin ˇ WindTracerŽ for Airports
In a day with a crosswind of 10 kts the wake from a previous aircraft will normall be clear within 30 seconds - why waste another 90 seconds of runway acceptance rate for a wake that is no longer there?
For safety a LIDAR system would be able to show the actual wake and significantly improve the acceptance rates on single mode runways and on multimode with a stream of takeoffs.