In good weather a helicopter is allowed to reduce it to 20 minutes.
In bad weather the alternate must be an airport with the facilities to conduct an instrument landing, so definitely not just a parking lot. And the forecasted weather at that airport needs to be good enough from 1 hour before until 1 hour after the expected arrival. "Good enough" is defined stricter for helicopters than for airplanes.
In bad weather the alternate must be an airport with the facilities to conduct an instrument landing, so definitely not just a parking lot. And the forecasted weather at that airport needs to be good enough from 1 hour before until 1 hour after the expected arrival. "Good enough" is defined stricter for helicopters than for airplanes.