I phoned CS and finally got a clarification from Airbnb:
" Bonjour Olivier,
Thank you for reaching Airbnb and also for bringing this concern to us. My apology for the misinformation for security deposit. This is Chrissie once again from Airbnb Customer Experience Team.
Just to recap of what you have called in you are clarifying in regards to policy for the security deposit as you also mention on Help Center it says that it is 14 days of the checkout date or before new guest checks in. Further checking our policy for Security Deposit stays the same that is you have 48 hours from your guest's check out date to make a claim on your security deposit.
For most reservations, 48 hours is enough time to allow hosts time to check their space before new guests arrive, and to help assure guests that any claims will be made in a timely manner.If more than 48 hours has passed, you can still request reimbursement from your guest through the Resolution Center. To open a Resolution Center request, visit:
www.airbnb.com/resolutions/new ."