Fiddle and violin are like identical twins and so you cannot tell one from the other. Actually, you should not even tell one from the other as they are the same thing. The only difference is the kind of music that you should play on any of them. In different settings, a violin is going to be referred to as a fiddle, for example, when it is used to play folk music. Just be clear in your mind that when you hear fiddle and violin, they mean the same thing. When used in classical music, then it becomes a violin. This is why it cannot be referred to as just the fiddle or the violin. It is all in the style of playing.
When I started playing the violin, my music teacher taught me to replicate the composer’s music to the letter, and in everything else too, including tone. This means that whatever classical piece I decide to play, I cannot in any way stray from what the composer has put down. It is what we could call a perfect imitation. It is because of this perfect replication that we would pull of a perfect presentation while playing 20 violins at the same time. As a violin player, you hold the violin in a special way so that you can enhance the playability as much as possible.
But a fiddle player is like a creative writer who portrays whatever he wants in his creation. This means that a fiddler will play a piece anyway he/she likes, or according to his own interpretation. So, how a fiddler pulls off a performance entirely depends on how talented he is. In addition, he/she might hold the fiddle anyway they feel most comfortable without caring whether there is some enhancement in the sound or not.
Another difference setting the two apart is that the fiddle can be accompanied by other instruments like the guitars, drums, electronic keyboards and many more. However, when used as a violin, only a few instruments would be in sync with the violin. These include the banjo, cello, viola, symphony horns and other violins of course.
A fiddle may actually have a fifth string for playing the viola, fancy that, making it a little different from the violin. However, this extra string will sooner or later be reproduced in the violin, so it is not much of a difference after all.
How much time would you take to play the instruments? Most people wrongly assume that you would take longer to know how to play the violin, but the truth is that fiddle and violin could take you the same time to learn since they are basically and structurally the same instruments.
As for style … hold the violin strictly between your chin and shoulder for the best projection of sound. That rule does not matter with the fiddle.
We can infer many other things from the fiddle and violin, but when you learn to play the fiddle, you can definitely practice further to play the violin. There is no doubt that you will have the best time playing either.