viabtc just accept 100 transaction each hour. So, you must submit your transaction on time like 5:00 or 6:00.
Viabtc is a shit, they are never going to accelerate your transaction. at the 00 of each hour there are more than 1000 users trying to accelerate their transactions.
You must have a quantum computer to be able to accelerate or just put your transacion in there before all the other people who is trying to do the same.
if you want to accelerate your transaction, just pay the fees, it is not difficult.