If the "agent" was your only point of contact and was the person through whom you paid the rent, you still could have sent the keys to them (same as rent). Anyway, not relevant.
"The landlord did not send the letter for refusing the security deposit by mail. He emailed it."I wasn't pointing to a "postal delay" as such; I'm just saying a court may not find it at all meaningful that you received it on 8/4. My point is that you're focusing on this 30 days like a laser when that's not necessarily productive.
"They are calculating the 30 days from the day the walk through was conducted ( 8/4 on their request) and not on 8/31 ( when the lease terminated and the tenants vacated )."Even though I believe you're referring to the state law that requires the landlord to send out X explanation for withholding a deposit within 30 days, I'm not sure what your point is here. Anyway, the clock on the 30 days starts running after you leave.
"So my original question is when does the clock for the 30 days start?"You've never actually made it clear what you're referring to here but, again, I believe you're vaguely referring to a state law requirement. If someone doesn't answer a question, they ... don't answer a question. There's no need to repeat it. :) At any rate, the timeline starts ticking when you move out, and you all are free to quibble over the relatively immaterial succeeding days. Who knows whether court will care.
"Why would the landlord enter the premises in the absence of the renter if the keys were not handed over?"This question doesn't make any sense. Re-read it. They know you moved out, right? :) They're free to visit/inspect the place even if you hadn't moved out, as a practical matter. "Doesnt it mean that the lease is over?"We keep circling back around to a relatively non-material issue, when you ought to be focusing on the topic of damages. That leads me to believe that you left these damages and you're thinking you can pin hopes of getting your deposit back and fending off any excess damage charges by lasering in on the fact that you didn't receive notice of the withheld deposit and charges until 10/4.
"No, there were no pictures taken either at move in or during walk through."Don't forget to do that in future. Still, the landlord will need to demonstrate to the court's satisfaction (whether you are suing for return of your deposit and/or they're suing you for excess) that it's more likely than not that you left the damages and this is what it cost to fix them (arguable on all counts).

