The tenant does not have the right to choose when you can enter the unit for showings to prospective tenants, and in this case the 24 hour written notice is not even required as stated under sec. 26(3) of the Residential Tenancies Act: Entry to show rental unit to prospective tenants (3) A landlord may enter the rental unit without written notice to show the unit to prospective tenants if, (a) the landlord and tenant have agreed that the tenancy will be terminated or one of them has given notice of termination to the other; (b) the landlord enters the unit between the hours of 8 a.m. and 8 p.m.; and (c) before entering, the landlord informs or makes a reasonable effort to inform the tenant of the intention to do so. 2006, c. 17, s. 26 (3). If the tenant refuses to co-operate, you could try calling the Rental Housing Enforcement Unit at 416-585-7214 and discuss this issue with them.