It takes anywhere from 20 to 60 seconds to get the status from my car (like if I want to know how charged the battery is).
I'm wondering if this is normal or something is wrong.
Yes it is normal. Not to get into details but there is no direct link between your OnStar RemoteLink app and your car. Here is how it works:
Now to the best of my knowledge, it takes a bit of time to do step 2 because it is a bit tricky to establish connection with a car that is not working. Remember your car doesn't stay connected to OnStar server all the time because it will drain battery and it will cost GM a bit of money to keep connection alive - GM uses cellular providers (AT&T and such) and they charge an arm & a leg for internet connection such as 3G and LTE.
In any case, 20-60 seconds to get an update from a car is normal.