It depends, 150 day of meditation can be different from one person to another. It depends also by the type of meditation that you have done, for example, did you follow the 40 day meditation program for beginners of HP Hooded Cobra 666? The final part about instructions for after the period of 40 days is very important. It is also important the Spiritual Warfare Training Program for Satanists.
If the Black Magick is against jews, the RtR direct on them can be very effective. Usually in Black Magick one person at a time to hit is better. First you should evaluate to do the Binding Spell and the Energy Ripping, especially if you have never done Black Magick before, but for extreme situations you could do the Destruction Ritual and you could use the Death Spell.
It is not a question of "when can I?" but of proper awareness of what you are doing. There is always this tendency to want to run with things.
It's not even five months, that's too little time. I have a feeling that you are not yet ready for Black Magic. If you were, you would not have asked such question.
150 days is short not only because you might be weak spiritually, but also because you might not have the right mindset yet and you may not understand the Morality. My advice is to study the main site, especially the Satanic Ethics. Meditate and reason on it and always ask yourself whether doing something is right or not from a Satanic perspective.