Can anyone provide instructions on how to get from this arena to the La Guardia area, particularly around 74th st/Roosevelt? Google maps says it cannot calculate. This would be around11:00pm at night.

The UBS website has good information for getting there in the main menu under 'plan your trip'

Take the LIRR from either the Elmont-UBS station or the Belmont Track station to Jamaica Station. Can take an E Subway or Bus from Jamaica Station

Trains run after events only.

Just take the cross island north

Thanks Andrew. Do these trains run all night?