MiniMe3388 said:
will it be more powerful?
90 days is usually recommended for workings that have to do with endings, such as workings to free the soul, or black magick.
For workings of white magick that do not have to do with endings in any way, I would recommend either cycles of 40 days (you do the working for 40 days, finish it, and then start it again a few days/weeks later on a suitable date) or a multiple of 40, like 80, 120, 160, 200, etc. days.
I usually go for 40 if I know it can be done a second time again reasonably soon after I finish the first cycle. I prefer doing clean and simple cycles in this way.
If you have a working that relies on a specific, very powerful date (like some rare planetary alignment that happens only once a year or smth) then you would be best off doing it for a longer amount of time, like 80 days. In the case of big workings that tackle something you want huge results with, you could even do it for a year straight or longer.