First pass yield???

// T is the table from your post...

[Pass 1st Time (%)] = 
var IDsWithEarliestDates = 
// First, get for all visible ID's
// their minimum start times VISIBLE
// in the current context(!!!).
    ADDCOLUMNS(
        DISTINCT( T[ID] ),
        "@MinStartTime",
            CALCULATE(
                MIN( T[Start Time] )
            )
    )
var CountOfIDsWherePassIsFirst = 
// Calculate the number of ID's
// where the result for the first
// visible date, as calculated above,
// is "pass."
    CALCULATE(
        DISTINCTCOUNT( T[ID] ),
        TREATAS(
            IDsWithEarliestDates,
            T[ID],
            T[Start Time]
        ),
        KEEPFILTERS( T[Result] = "Pass" )
    )
var CountOfAllVisibleIDs =
// Get the number of all visible ID's.
    DISTINCTCOUNT( T[ID] )
var Result = 
    DIVIDE(
        CountOfIDsWherePassIsFirst,
        CountOfAllVisibleIDs
    )
RETURN
    Result

Be careful - this formula is sensitive to all filters you put on the table, meaning it respects them all, so the calculation above is carried out within the visible set of ID's with all the restricting filters.