In Ontario rent is considered late as of midnight on the day the landlord and tenant have set it to be paid. Most landlords/owners will set payment date on the first of each month (assuming you and the renters are on a monthly basis).
So, rent is late, now what can be done? As a property manager I have a system in place that calls for an automatic late notice to be sent out. This protects the owner from waiting around for weeks for payment only to find it isn’t coming. After which you must still serve a late notice (N4) before filing with the landlord tenant board for an eviction.
Glenn Brown is owner of My Rental Unit property management and has enjoyed success with multiple unit investing.