In short four times a week for a month. You can prolong this if you so may wish, but it is not recommended as Smolov Jr is designed very unbalanced and is better used as a shock cycle rather than a solid program to build a basis. Therefore also consider different programs like Stronglifts 5x5 or starting strength if you are a beginning lifter. Two years or more experience would be a good fit for doing Smolov Jr.
If you do Smolov Jr there are four sessions a week with a range of 6 to ten sets per sessions. You can see the split attached in the picture and also download the Smolov Jr Calculator at the end of this post if you want to start the program. The calculator does everything for you based on your one repetition maximum and can be printed out in A4 landscape format.
You can do Smolov Jr back to back. Keep in mind that the program asks to do one lift only rather than distributing your work between all of the different lifts. If you do back to back cycles it is probably good advice to rotate between the different lifts.