JANUARY: Problem at Sea
No references, except a character mentions not having met another character in seventeen years, “not since the war”. If we assume that a meeting took place in the middle of the war, 1915, this story would be set in 1932. Since Poirot often travels to warm places in winter, January is possible.
FEBRUARY: The Adventure of the Western Star
JULY: Dumb Witness
There's no mention of Bella or the Argentine, so it could be set before Murder on the Links. Charles Arundell is attempting the world water speed record, which wasn't officially established as a record category until 1928, so it's probably after that (according to Wikipedia). Wikipedia also says the last serious UK challenge of the 1930s was made in July 1932 by Kaye Don, so this might be the Poirot universe's version of that.