In standard SQL you can specify where to put nulls:
order by col asc nulls first
order by col asc nulls last
order by col desc nulls first
order by col desc nulls last
but T-SQL doesn’t comply with the standard here. The order of NULLs depends on whether you sort ascending or descending in T-SQL:
order by col asc -- implies nulls first
order by col desc -- implies nulls last
With integers you could simply sort by the negatives:
order by -col asc -- sorts by +col desc, implies nulls first
order by -col desc -- sorts by +col asc, implies nulls last
But this is not possible with dates (or strings for that matter), so you must first sort by is null / is not null and only then by your column:
order by case when col is null then 1 else 2 end, col asc|desc -- i.e. nulls first
order by case when col is null then 2 else 1 end, col asc|desc -- i.e. nulls last