My former classical violin teacher, mentor and friend, the late and widely beloved Michael Davis, told me many things which influenced me early on as a classical musician and later came to influence my growth as a jazz player.
Regarding the amount of time spent practicing daily, he felt that, "if you can't get everything done in three hours, you're not practicing efficiently". In his view, the saying, "practice makes perfect", wasn't adequate. Better to adapt the mantra, "Perfect practice makes perfect".
Many of my students at Berklee and abroad come out of a classical tradition and have developed practice habits conducive to making gains as a technician and classical player. Often though, these same habits become detrimental to growth in "creative studies". This is not to suggest that practicing technique and jazz/ improvisation are mutually exclusive; quite the opposite is true.
It's actually advantageous to consolidate improvisation practice with technical practice. For example, one can focus on technical issues such as string crossing, bow control, intonation, double stops, etc. all while improvising- this is the equivalent of killing two birds with one stone, and offers the added advantages of 1)developing technique beyond the "given" and limited possibilities of the classical repertoire and 2) providing the student w/ a sense of ownership in the vocabulary he/she is practicing/creating.
However, you must remember that regardless of how many years you have studied your instrument and/or classical music, the moment you begin to study jazz and/or improvised tonal music, you are a novice.
Accepting this is difficult, because you have come to identify yourself as an expert. Both can be true, i.e., that you are an expert musician and instrumentalist, and at the same time a novice in jazz or improvised tonal music. In studying improvisation or jazz, you are embarking upon a journey to obtain an entirely new and different skill set. It will take time. (In his 2008 book, Outliers, Malcolm Gladwell refers to a study which holds up the "10,000 hour rule", i.e., it takes about 10,000 hours, or 10 years at 3 hrs per day, to effectively master any given discipline. Even accounting for your accrued mastery on your instrument, you might want to allow yourself about 6 years.) I've referred before to the difficulty and discomfort that comes out of accepting your new status as a "novice". For many musicians switching from classical to jazz, this discomfort is intolerable. It can threaten one's self esteem and cause all sorts of defensive thoughts/behaviors to arise. One of these is denial. The sooner you accept the truth about where you are in your development and get over your insecurity, the sooner you can begin to make progress.
Remember, you can still take credit for the mastery that you have developed over years of
practice. You have a lot to be proud of in taking the plunge into something new. Ultimately, by forging ahead in a discipline which is totally new to you, you will come out stronger for it.
One of my favorite and most accomplished young adult students frequently arrives to his lesson with a list of concerns and questions including things such as sound production, shoulder rests, philosophical questions about the state of the mind while playing, posture, et al. These are all very good questions for a classical student, but often they strike me as distractions for a jazz student. Every week, as he plays solos for me over standard tunes, a large part of the things that I notice holding him back are related to gaps in his grasp of harmony, i.e. "playing the (chord) changes". Sure, there are other things worth working on as well, but this is a consistent thing that comes up which he continues to evade. It's not that he can't execute ideas on the violin- it's that he can't Conceive of the ideas because the harmony is challenging and eluding him. I continually give him exercises for internalizing the harmony, and he continually avoids doing them. Is this denial? Why do so many of us have this same tendency, I wonder. I have to be ever vigilant in my own practice to make sure I'm not "practicing" what is comfortable, but rather addressing the gaps, the uncomfortable areas. Every day you practice you are faced with one crucial challenge, which is to practice effectively. Make it count. Practice the things that matter. Michael Davis once also told me, "if you sound good, you're probably not practicing". Most of your practice time should be devoted to things which you don't sound good doing. Once you sound good, it's time to move to something else.
Their are several ways you can go about drilling harmony such that, over time, you assimilate and internalize the information (and once you have internalized harmony, the understanding will never go away.) I've covered many of these in other articles, but to recap:
1) articulate the chords on the violin in various forms (as double stops or arpeggios in all inversions or shapes)
2) play the voice-led chords on the piano (or guitar)
3) when you listen to music, Focus on listening to the harmony instead of the melody. Try to use your ears to transcribe the harmony on any music you listen to.
4)play voice led arpeggios or double stops of chord progressions (including both chord pairs and/or longer progressions)
5) harmonize melodies and/or solos in double-stops (both as parallel thirds, 4ths, 6ths, 7ths, 2nds, and as non parallel harmonies)
6) play 3rds and 7ths of chords in various comping styles. Play root/3rd/7th voicings of chords.
Play voice-led upper extensions of chords. Walk bass lines.
Importantly, one's brain is typically only able to handle this kind of practice for so long. Perhaps an hour tops. So, if you practice 2 hours in a day, you might want to spend 1/3-1/2 of your time drilling these harmonic issues. The rest of the time can be spent on other things. But if you ignore this practice, you are just stalling, and Nothing can replace real harmonic understanding.
It will never come easily, and there's no way around it. You have to practice the important things or you will just be living in denial, and on some deep level, you will be frustrated. On the other hand, make these a regular part of your practice and you will see results over time. The rewards are worth it.