This has been rather common recently until 31 Jan, given that the nominal flight time has been successively lengthened to 18:20 as compared to an original 17:30 (it is 17:50 now). FR24 lists the flight of 15 Oct 2017 with a flight time of 15:54 (arriving 2:11 early), while for the previous day the flight time is reported as 18:57 (arriving 0:55 late) [the flight routes differ substantially].