Hello :)
I am still fairly new to this way of thinking which is based in gratitude rather than lack so I can only answer from my rather recent experiances.
Sorry, I cannot give you a set time... I wish that I could
It depends on numerous factors... one being pre Existing attitudes you have regarding manifesting. I had and still have quite a numerous layers to clear surrounding my.attitudes to manifesting my dreams... I found affirmations to be quite helpful to clear these though...
"I am worthy of xyz',
"The universe always provides me with what I need"
"I am deserving of my dreams"
Really whatever feels right and works.for.you :)
Also things do take time on earth... my guidance frequently reminds me that the more space I give the universe to work.its magic, the easier it is to manifest.
Usually what tends to happen though is once you start to shift your focus to gratitude is that you begin to live fully in the present... so in this present moment... you are being provided with everything you need... this is where belief starts to come in...
What happened to me is I started to really feel what is available to me ... which of my dreams are completely aligned with my destiny, once I understood my destiny, I understood that my most authentic dreams are present because they are in fact already part of my future and I am slowly progressing towards them... without consciously having to stress too much about it.
About a year ago I had a miny epiphany... my guidance told.me that "I don't need to stress or worry because The universe already knows my hearts true desire"... its easier to manifest when we are relaxed.
Peace to you :)