Although im not a new magician it seems like a noobish question . About how long should one wait to perform a spell if you recently performed one and not getting or seemingly not getting the results you want or expect?
The same goes for evocation can you stack the numbers of demons or angels you evoke that do similar things or should you do one that specializes in that area at a time (like if i evoke 5 demons in one night is it best that they have different specialties?)
Work with one at a time for each goal so that they do not interfere with each other UNLESS they have complimentary ways of working together, like the example of Raphael (who brings down Divine Light from above) and Marbas (who brings in earthly power from below) for healing given in Evoking Eternity. In fact, if you are looking to work with multiple entities for a single goal, I’d recommend you read the chapters on evoking legions in EE. Multiple demons are especially useful in baneful workings.
As for how long to wait? It varies, due to the different variables needing to be rearranged to bring the goal to pass. If you have seen no movement within a month, evoke the demon and ask for a status report. Perhaps it has encountered something that is taking time to overcome.
My opinion for what it’s worth:
If something fails outright, do some divination to find out why it didn’t succeed, if you keep going there may be a reason you don’t want that thing or why it would be harmful, and some entities could actually be looking out for you by making sure you don’t get it, or don’t get it yet.
Yes, you can “stack” evocation, invocation, all sorts but it’s best done under the auspices of one entity who will then 1. direct you to the entities you need, instead of you trying to choose and 2. command them directly himself/herself, which is more effective than trying to micro-manage the process yourself.
The first one I knew for ages, the second one I’m just learning in the past few months because I never tried to evoke more than one entity towards a task since I was a child, but following on from some of my experiences when I invoked Ahriman I’m seeing different ways of working that include this.
Just my experiences here though so there may be other and better answers.