Finite-time MLE of the forced secular ISS over 5 Gyr for different degrees of truncation of the Hamiltonian and the corresponding Lyapunov time FT-MLE⁻¹. The bands represent the [5th, 95th] percentile range of the PDF estimated from ensembles of 128 (ℋ_2n) and 1148 (ℋ) stable orbital solutions with very close initial conditions. The black lines denote the nominal solution 𝒮 for nine different initial tangent vectors.