No the beacon interval cannot be changed from the meraki dashboard. They fixed it at 100ms and is not configurable by administrators.
But you can do few things to reduce air time,
- Disable low data rates
- Prefer 5Ghz/6Ghz
- Adjust Minimum Bitrate per SSID
- Tune TX Power and channel width
And keep this in mind,
Changing beacon intervals can;
- Break roaming behaviour
- Cause battery drain on mobile clients
- Create inconsistent RF behaviour across APs
Let me know the use case for more relevant answer