Unfortunately you can not schedule a publishing of an asset. as you may already know you need to publish a page in order to publish an asset and you can schedule the publishing of a page.
What you can do is make changes to an asset, approve it, then schedule a publish on any page that uses that asset.
Give it try, Just remember for every page you would like the changes to the asset to apply to you will have to schedule publishing.
To clarify my last post, you CAN schedule publishing on Image and file assets.
Having the ability to schedule publishing on all assets, scheduling a full site publish and/or the ability to schedule publishing for pages in bulk are all great ideas you can post on the community.