How long do I have to wait for a manifestation of an evocation? I evoked a spirit to free me of my obstacles, and so far I’ve only feelings its working and no real substantial change in the physical. I evoked it twice once to issue the task then a second because I felt I needed to. Its been a week, but how long do I have to wait? Its very powerful, and don’t these things happen very quickly?
That’s like asking how long is a short piece of string - there’s no DEFINITIVE answer.
Because the wheels of causality that may deliver your result, hopefully WILL, may take time to set in motion.
Practical answer, ask the spirit to send you SOME sign you can recognise within a week that they’ve undertaken to deliver this, and will do so.
If that happens, you have to sit tight and wait, confident it’s on its way; if not, back to the drawing board I guess?
Remember that you’re trying to change reality with your mind and your will, that’s the action of a god (or, godlike being) - ease up on it, on yourself, and keep honest records (no wishful thining or “maybe it was a lesson”) but at the same time, have faith - in yourself. 
your desire of the outcome will hold you back. cause if you have a desire for something. what does that enforce? you don’t have it! the desire of something just reinforces that you don’t have it.
heres a link to julien blancs video about letting go of desire. https://www.youtube.com/watch?v=MU1Rp184IT4
watch this and follow his meditation exercise.
and watch a couple of his videos as well explaining why what you desire most you have to let go of It to get it.
hope this helps you. please update with results