If the landlord is allowed to enter to show the property, this will probably extend to the landlord's agents as well. Your rental agreement controls. You need to read the agreement to determine the extent of your rights and obligations.
You can reach Harkess & Salter LLC at (303) 531-5380 or info@Harkess-Salter.com. Stephen Harkess is an attorney licensed in the state and federal courts of Colorado. This answer is for general information only and does not create an attorney client relationship between Stephen Harkess or Harkess & Salter LLC and any person. You should schedule a consultation with an attorney to discuss the specifics of your legal issues.
The language in your rental agreement will control, there is no law that trumps the agreement, unless the agreement is illegal etc.
If the agreement says that the landlord can enter that will allow his agent, the REALTOR, to enter under the same conditions.
"Reasonable time and days" does not include placing a lockbox on your door for access at will. You pay rent for the right of exclusive possession of the property, so the landlord nor his agent may enter your property without proper notice as described in your lease. Additionally, showing your home to perspective tenants 5 months prior to the end of your lease is not reasonable.
If you cannot make the landlord listen to your demands I recommend consulting an attorney for assistance.
Donald at Robinson and Henry, PC at (303) 688-0944 or Donald@RobinsonandHenry.com. The above information is provided to you “AS IS,” does not constitute legal advice and we are not acting as your attorney. Because we do not have a full view of the facts in providing the above information we make no claims, promises or guarantees about the accuracy, completeness, or adequacy of the information contained in or linked to this web site and its associated sites. Legal advice must be tailored to the specific circumstances of each case and the information provided to you may not be an appropriate fit in your case. Nothing here is provided or should be used as a substitute for the advice of competent legal counsel. This postings is for educational and information purposes only, not legal advice or legal opinions. The information is not intended to create a lawyer-client relationship between the author and you.