With every new keyboard, it will take some time to get used to it. I used both SwiftKey and Swype for a few months. Both have symbols in different locations. The Google keyboard has symbols in locations different than the other two and it also is taking me some time to get used to it.
I find that with every keyboard I have ever used, whether physical or virtual, it takes at least a week and most likely around 3 weeks to really get use to. The amount of time depends on how different it is than the other ones I am used to. I have to commit to using it consistently for that period of time before I feel I can give a meaningful evaluation of a keyboard.
Well everyone is different and for me I can notice it right away. I didn't like swype or swiftkey from the beginning. I liked the stock keyboard except for the fact that auto correct was missing. I could tell immediately that I liked the Google keyboard more than the others