Yes that is true. Bitcoin price is not fixed as it is volatile to its price and it can be change anytime without having a schedule to follow.
We can't perfectly predict the increase or decrease in bitcoin price because that is impossible but at least having a chance of doing right is possible by analyzing different news about bitcoin whether it is good or bad, if good news are more than bad news then it will be a increase and if the bad news are more than good news then it will be a decrease. You can also analyze the price chart where you can find patterns that can make your decisions right.