How to calculate suicide burn altitude for craft in Vizzy?

Assuming your algebra is solid, you could also integrate this equation with the equation @RudimentaryCheezit provided to get a burn time. Also, the acceleration due to drag is listed under Craft Information >> velocity in Vizzy, so you should be able to implement that into your equation as well

((A x g) + ½v²) / a

A is the altitude of your lander (ground level)
g is the acceleration of gravity in m/s²
v is the velocity of your lander relative to the surface (because planets spin)
a is the acceleration of your engines at maximum throttle, which is equal to engine's thrust / lander mass

the AI that produced this formula (bing chat) cautioned that the burn should begin slightly earlier, assumes there is no atmosphere, and disregards the lander's mass decreasing as the engines consume fuel