No you don't, and yes you do. Basically, you have to keep submitting until you see the "success" message. If you see an error message then the server is too busy, try again. If you see the "submission limit reached", then you have to keep trying or you missed the hour mark and have to wait another hour. As long as it says successful, it has been submitted and you just need to wait until viabtc mines the next block. Also, assuming your tx was in a queue short enough to be included. I have seen it been included in the second block mined. Guess lots of people lining up to use viabtc these days.