I tried it my friend it says "Submissions are beyond limit. Please try later. "
Yes, since it is a popular tx accelerator, alot of people use it. You need to wait until viabtc finds a block, and then immediately enter your transaction into it.
You can check their blocks here,
https://blockchain.info/Also, I'm sure you would be able to run like an imacro to insert your tx, not sure if that's allowed.
You should ask the guys in the thread i linked above how they exactly do it.