Find the website of a university providing Russian courses, which is close to your area. Check how many hours this Russian course includes. Multiply this value by 3 or 5 because the students should also do a lot of homework and you'll get the desired total number of hours to become proficient enough to carry a conversation. If you'll spend 5 hours a week then divide the total number of hours by 5 and you'll get the number of weeks. This, of course, would work only if you will struggle with Russian as hard as the students of that university do.