If acceleration was successful, ViaBTC tells you. If it doesn't say anything, something probably went wrong.
I tested this 4 times today. All were at the whole hours.
ViaBTC doesn't show any message when the acceleration is successful. Maybe something is wrong from my side.
When I submit a transaction late, it says "Submissions are beyond limit. Please try later."
From my understanding, whenever it doesn't show any message, it means that the acceleration is successful. Because when I submit a same transaction a few minutes later (when the 100 transaction limit has definitely been filled) again, it says "This transaction is being accelerated."
It's been a while, but I remember it adding the word "already" if that's the case.
No, it only says "This transaction is being accelerated."
You can test it with
the random transaction I submitted some minutes ago. (If it isn't confirmed before you see this post, off course.)