The reason I want to use a variable is so that I can use the same cut off time in multiple queries to make sure to make sure that I don't get records in one query with a later date than another.

For example

CREATE OR REFRESH LIVE TABLE filtered_one
AS SELECT * FROM my_table_one
WHERE created_at > current_time();

CREATE OR REFRESH LIVE TABLE filtered_two
AS SELECT * FROM my_table_two
WHERE created_at > current_time();

If I want to compare records in `filtered_one` to the results in `filtered_two` I can't rely on them having used the same value for `current_time()`.