Frequency depends on your goals, schedule, and timeframes, and my availability.
For example, if you need to take a Russian test in two months, and your current level is pretty far from your target level, you may need to take at least one hour a day.
If it is just a maintenance for your current advanced level, it could be one lesson every 2-4 weeks.
For most learners who focus on the steady progress in Russian, it is 1-2 hours per week.