The landlord can NOT charge for their own time, including the time of any staff on payroll (e.g. a superintendent or building engineer). They may only charge for the time billed to them by outside contractors, companies, etc., and they may bill you the actual amount billed to them--though they can't charge you a clearly excessive amount, so you could challenge it if either the rate or the hours seems too high. If they've already given you back your security deposit, you can ignore their claim for money until and unless they sue you--then you'd have to defend yourself, but they'd have to prove their claim. If they are withholding some or all of your security deposit, you may bring a lawsuit (including in small claims) for its return and the landlord would have to substantiate the amounts taken out.