Can I Show Multiple "WHERE" Filtered Results In A Single Query/Output Table?
I think you are looking for conditional aggregation:

SELECT b.WorkflowID,
       count(case when a.creationtime &lt;= timestamp '2015-06-10 14:00:00' then b.worflowid end) as count_before,
       sum(  case when a.creationtime &lt;= timestamp '2015-06-10 14:00:00' then (LENGTH(b.data)/1024.)::numeric(10,2) end) as size_before
       count(case when a.creationtime &gt; timestamp '2015-06-10 14:00:00' then b.worflowid end) as count_after,
       sum(  case when a.creationtime &gt; timestamp '2015-06-10 14:00:00' then (LENGTH(b.data)/1024.)::numeric(10,2) end) as size_after
FROM Table1 a
JOIN Table2 b
  ON (a.WorkflowID = b.WorkflowID)
GROUP BY b.WorkflowID;