This is the 3350th most frequent Polish word.
wczesnym
"Early" (in the instrumental case).
The word "wczesnym" is used here as an adjective in its instrumental form, agreeing with "rankiem" to describe "early morning."
Wczesnym rankiem wybrałem się na spacer nad jezioro.
Early in the morning, I went for a walk by the lake.
"Wczesnym" functions as an adjective describing "latem," indicating the initial period of summer.
Wczesnym latem kwitną dzikie kwiaty na łąkach.
In early summer, wildflowers bloom in the meadows.
Here, "wczesnym" is an adjective in the instrumental case, modifying "etapem" to describe the stage as occurring early in a sequence.