Experience has shown that after watering - in the best case due to an expected rain shower - it takes about five in exceptional cases 10-12 days until a visual change is visible. The lawn now looks fresher and stronger again.
With regular application, the changes are not so visible because the lawn is always fresh and green.
If no differences are visible at all, there may be various reasons for this:
It is possible that the Fertilizer quantity too low
Maybe the lawn has a fungal disease
Lawn thatch can also be a cause
The soil is so heavily compacted that dry patches form