Figuring out how long it takes to land on a planet

I need help with understanding what details one should consider when computing the time it might take for a fictional spacecraft to make landfall from orbit. I’m sure its mass and engine velocity have bearing on this, especially since this vehicle does not rely on atmosphere to brake its descent. If I know the weight is X and the descent engines provide Y amount of thrust, and I know the gravity of the planet on which it is landing, are there other factors at work to consider?