You must follow the normal timing permissions and restrictions for the exiled card. If it’s a land, you can’t play it unless you have land plays available.

You’ll still pay all costs for a spell cast this way, including additional costs. You may also pay alternative costs if any are available.

Rooting Moloch gives you permission to play the card as a land or cast it as a spell. You can’t cycle the exiled card.

If you don’t play the exiled card, it remains exiled.