Impressionism (According to Wikipedia) is:Impressionism
is a 19th-century art movement
characterized by relatively small, thin, yet visible brush strokes, open composition
, emphasis on accurate depiction of light in its changing qualities (often accentuating the effects of the passage of time), ordinary subject matter, inclusion of movement
as a crucial element of human perception and experience, and unusual visual angles. Impressionism originated with a group of Paris-based artists whose independent exhibitions brought them to prominence during the 1870s and 1880s.
So, 1870's - 1880's. Then I just came across this oil sketch by Constable which was done in 1810 (so around 60 years earlier). It looks so modern!