Question: Eval time of vertical drop of a function

Hi everyone 

I am trying to solve the following problem. I want to evaluate the time when the function Sx(t) drops (the last vertical drop at about 0.45 sec) 

The minimize command doesnt work because the function slightly deacreases afterwards but I am interested in the drop. For a miniization (evaluate the relevant time). I do it as follows:

Does anyone have an idea how to evaluete the time of drop? Is there an other command than minimize to solve this? 

Thanks in advance!

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