I would expect a single point addition operation (P₃ = P₁ + P₂) to have a very predictable machine cycle count.  It should be something like:

x₃ = λ²+a₁λ−a₂−x₁−x₂

y₃ = −a₁x₃−a₃−λx₃+λx₁−y₁

λ = (y₂−y₁) / (x₂−x₁)

From:  https://crypto.stanford.edu/pbc/notes/elliptic/explicit.html