In the case that a tenant owes rent or other easily determinable charges, it is safest to send the letter as soon as practical and bill them separately for other damages.
Returning keys may or may not be important in establishing the date the clock starts rolling. More importantly is when did you know they were out and what was the termination date of their agreement.
§704.28 (4) (b) was a big change. Let’s say a tenant on a year lease vacates four months early, depending on when the unit gets rerented, the 21 days could start up to four months after they vacate.
This also applies to month to month occupancies. If the tenant moved without notice, the notice date is implied to be the date the owner learned they moved out.
I look at (4) (b) as more of a safety net for owners that are sloppy in their response times or did not know the date the tenant vacated. A far better approach would be to send a deposit transmittal letter as soon as you learn they left before the end of the agreement, stating the deposit is being applied to the rent due and that they are liable for the rent until, for example, Feb 29th, 2016 unless the unit is rerented prior to that date. Also note that you are attempting to rerent the unit.
Even if (4) (b) keeps you from losing a deposit lawsuit, it probably does not keep you out of court as tenants still believe the 21 days start the day they left and not the last day of the lease that could be months in the future.
I feel it is very important when a tenant owes rent equal to or more than the deposit that you limit the deposit withholding letter to the rent with a notation that they are being billed separately for other damages. If you have late fees in the written agreement those too can be part of the undisputed deposit withholding letter. [EDIT: Attorney Tristan Pettit points out that I was not clear that late fees must also be included in the non standard provision. ]
There have been a few cases, including an outstate unpublished appellate decision, where the courts have doubled the wrongfully withheld items on a deposit transmittal letter and then applied that to a determination of double damages and attorney fees even though the rent alone exceeded the deposit. For example the tenant has one month’s rent as deposit and leaves owing a month’s rent. The landlord, being angry they left in the middle of the night puts $500 charge on the deposit letter for changing the locks. Tenant now is also angry and takes the landlord to court. Some courts will mistakenly double the wrongfully withheld $500 and then clip the owner for the tenant’s attorney fees on top of that. Had the deposit letter just had the rent due on it and the owner billed the tenant for the questionable charges it would not have made the owner any less of a butthead, but he would have some money left to sign up for meditation or anger management classes.
You should also use the separate bill method for other things that are legit, but cannot be deducted from the deposit such as carpet cleaning if written into the rental agreement. Note that our company does not change for carpet cleaning, but the WI Attorney General has said you may, as long as you do not deduct the charge from the deposit.
704.28 (4) Timing for return. A landlord shall deliver or mail to a tenant the full amount of any security deposit paid by the tenant, less any amounts that may be withheld under subs. (1) and (2), within 21 days after any of the following:
(a) If the tenant vacates the premises on the termination date of the rental agreement, the date on which the rental agreement terminates.
(b) If the tenant vacates the premises or is evicted before the termination date of the rental agreement, the date on which the tenant’s rental agreement terminates or, if the landlord rerents the premises before the tenant’s rental agreement terminates, the date on which the new tenant’s tenancy begins.
(c) If the tenant vacates the premises or is evicted after the termination date of the rental agreement, the date on which the landlord learns that the tenant has vacated the premises or has been removed from the premises under s. 799.45 (2).