Moonstar is right, you'd be very lucky to find any meadowsweet still flowering, they usually flower through the summer and are over by early September.
But for future reference, the flowers of meadowsweet and hemlock are really very different. Meadowsweet flowers in a fluffy cloud, with irregular flowerheads containing hundreds of tiny flowers. It also smells very sweet.
Hemlock flower heads are much more regular, forming "umbels" (like umbrellas) where individual flowers grow in clusters at the end of stalks which all radiate out from a single point at the end of the stem.
Looking at the images available on the web, a lot of the hemlock flowers are pictured from above, so the difference is less obvious.
The leaves are also very different. Meadowsweet has serrated leaves growing in pairs up the stalk, with three or five leaves being fused together to make the terminal leaf and the end of the stalk.
Hemlock leaves are very deeply cut, lacy and fern-like.