I would like to set my land to midnight for all who visit. What is the command for land card?

[Rolig Loon]

That depends on what sort of "land" you are talking about.  If you want to set windlight settings for the entire region, and if you are an estate manager, you can do that in World >>> Region/Estate >>> Environment.  If you want to set them for a parcel only, you can do that if you are using the Firestorm viewer.  Changes are made in the parcel description field in World >>> About Land >>> General  (there is no "land card").  See the instructions at http://wiki.phoenixviewer.com/fs_windlight . 

[Rolig Loon]

That depends on what sort of "land" you are talking about.  If you want to set windlight settings for the entire region, and if you are an estate manager, you can do that in World >>> Region/Estate >>> Environment.  If you want to set them for a parcel only, you can do that if you are using the Firestorm viewer.  Changes are made in the parcel description field in World >>> About Land >>> General  (there is no "land card").  See the instructions at http://wiki.phoenixviewer.com/fs_windlight . 

[Alwin Alcott]

as small addition to the answer of Rolig:

 

you can't force anybody to see your windlight settings as you want. In the viewer it's possible to keep the own settings and overrule the sim/parcel settings

[ChinRey]

Just to add one detail to Rolig's answer, the parcel windlight you can set with Firestorm will only work if the visitor also uses Firestorm (or a Firestorm based third party viewer), other viewers will just ignore that setting.

But Alwin's answer is the significant one here: it is not possible to force anybody to use a specific windlight.