query = """
SELECT
    DATE(df1.timepoint) AS timepoint
    , DATE(df2.from_date) AS start
    , DATE(df2.to_date) AS end
    , df1.measure AS measure_a
    , df2.measure AS measure_b
FROM
    df1 
INNER JOIN df2
    ON df1.timepoint BETWEEN 
        df2.from_date AND df2.to_date
ORDER BY
    df1.timepoint;
"""
Can one use comparisons to merge two pandas data-frames?