Is it considered allowed to set aside the full amount of Khums on the anniversary day but delay the actual payment until one is able to travel and physically deliver the Khums to the Marja's office rather than pay through a local charity?
It is obligatory to pay the Khums as soon as possible with out any delay. If you are in a place where you can not deliver the Khums to the Marje' of Taqleed or any trusted person who is authorised by the Marje' to receive, means that you no way to deliver the Khums, then you can wait but try your best to find a safe way to deliver as soon as you can. Delaying or postponing Khums delivery with out serious reason is not allowed.
Wassalam.