At first it would be probably one tutorial a month, this would not be however set in stone, there is some le-way, in reguards to Real Life issues.
If for example there becomes a greater demand for tutorials, you may be expected to do a few more, it all depends on how many people wish to apply for the role and how many are committed enough.
I will point out that to earn your "Staff" badge, significant proof of your commitment would be required, and this would be awarded completely under the disgression of the Directors
However, if you can show progress and that you are committed to the role. then there won't be a problem.