This is the 13923rd most frequent Turkish word.
marketlerin
"Of the markets" or "markets'" (possessive form of "markets" in Turkish).
In this sentence, 'marketlerin' is the possessive form (plural, third-person) showing ownership of the opening hours.
Marketlerin açılış saatleri sabah 8'de başlar.
The opening hours of the markets start at 8 in the morning.
Here, 'marketlerin' indicates the location associated with the markets.
Marketlerin olduğu caddede yürüyüş yaptım.
I took a walk on the street where the markets are located.
In this case, 'marketlerin' again shows possession but refers specifically to the pricing policies of the markets.