Welcome to the Airtable community!
Are they lookups in the same field? If so, you can use a rollup field.
However, because you have several different fields , I’m guessing a rollup won’t work for you.
Here is a different formula designed for four different date/time fields. You can extend the pattern to add more date/time fields. Note that it might not work for lookup fields, because lookup fields are quirky. You might also need to set the timezone formatting options on the formula field.
IF(
OR(
{Time 1},
{Time 2},
{Time 3},
{Time 4}
),
DATETIME_PARSE(
MIN(
IF({Time 1}, VALUE(DATETIME_FORMAT({Time 1}, 'x')), 999999999999999),
IF({Time 2}, VALUE(DATETIME_FORMAT({Time 2}, 'x')), 999999999999999),
IF({Time 3}, VALUE(DATETIME_FORMAT({Time 3}, 'x')), 999999999999999),
IF({Time 4}, VALUE(DATETIME_FORMAT({Time 4}, 'x')), 999999999999999)
) & "",
"x"
)
)
