Can a tenant refuse to let an agent onto property after receiving 24 hours notice? The lease does not cover the issue.

During the pendancy of the lease, and for all intents and purposes, the home and the land it sits on "belongs" to your tenant, and you have no "right" to invade your tenant's "quiet enjoyment" of the property. The tenant may allow, or disallow, anyone he or she wants onto the land or in the home. You can tape a "request" to the door and ask the tenant, very nicely, to call you about the situation, but don't be surprised if he / she says "No." This also depends on what the lease says and the terms of any state statutes.