Tortoises absorb toxins through their skin, so if you treat the yard, you'll have to keep the tortoise off it. I don't have an answer to your question, sorry.
I use a perimeter granual ... I buy it from DIY pest... First I treat the entire yard then every two month I go around the perimeter... Directions say its safe after watered in..... And it works.. Haven't seen a tick in two yrs.. On me or my dogs..lol