Question: Chance of Arrival in Unit Reinforcement

[Imp]

Rough guide the lower the chance the larger the range.
Rough guess
20% chance > by turn 3 a bit over 50% chance it will turn up.
10% increases the range dramatically around 27% chance of turning up on turn 3.
Turn 6 will be around 50% chance of turning up.
So 10% probably gives a good likelihood of turning up between turns 5-9.
You could do the maths if want accurate chances.