If it is a lot i will use Volcarona's flame body:D
Tirtouga Eggs hatch in 30 Egg cycles.
Generation V/VI 7710 steps
Generation VII 7680 steps
Generation VIII/IX 3840 steps
List of Pokémon by breeding attributes (Bulbapedia) Decreasing Egg cycles (Bulbapedia)
It takes 7,680 steps. Like you said, it's wise to use flame body to make things faster.