Some symptoms or problems can improve within a day.
Others could take a week or more.
In mood and anxiety disorders, and in other struggles towards life improvement, many significant changes or improvements can take several months.
With this kind of time scale, it can be hard to perceive any change happening in the present moment.
So, consider this analogy:
Let your symptoms or problems be represented by an empty 4-litre milk jug.
Let your efforts to improve your symptoms or problems be represented by a dropper, which will add individual drops of milk to the jug. Each major step towards substantive change is represented by a full jug. In many ongoing processes of life change--such as dealing with chronic depression--you may need to take repeated such steps, but I think each single step can be very important and significant.
A single drop is about 1/20th of one millilitre in volume. So, in order to fill the jug, you will need to add 80 000 drops.
In order to add 80 000 drops in about 2-3 months' time, you will need to add about 1200 drops per day, or 50 drops per hour, or about 1 drop per minute.
This is the rate to keep in mind with regards to substantive life change -- it is like adding 1 drop per minute in order to fill up a 4-litre milk jug. The moment-to-moment pace may seem slow, but it is not imperceptible, as long as you have a way to visualize it. Keep using your dropper. Be patient.
(To extend this analogy a bit further, I guess we should say that it is important to make sure your jug doesn't have any leaks -- many therapeutic efforts cannot catch up with what is lost from a leaky jug! Leaks may be caused by chronic stresses, addictions, unaddressed physical health problems, unhealthy relationships, etc. )