We Demonstrate That An Interferometer Based On Modulated Magnetic Field Pulses Enables Precise Characterization Of The Energies And Lifetimes Of Efimov Trimers Irrespective Of The Magnitude And Sign Of The Interactions In Rb85 Thermal Gases. Despite Thermal Effects, Interference Fringes Develop When The Dark Time Between The Pulses Is Varied. This Enables The Selective Excitation Of Coherent Superpositions Of Trimer, Dimer, And Free-Atom States. The Interference Patterns Possess Two Distinct Damping Timescales At Short And Long Dark Times That Are Either Equal To Or Twice As Long As The Lifetime Of Efimov Trimers, Respectively. Specifically, This Behavior At Long Dark Times Provides An Interpretation Of The Unusually Large Damping Timescales Reported In A Recent Experiment With Li7 Thermal Gases [Yudkin Et Al., Phys. Rev. Lett. 122, 200402 (2019)]. Apart From That, Our Results Constitute A Stepping Stone Towards A High Precision Few-Body State Interferometry For Dense Quantum Gases.