This is one of the two clearly identifiable but irreconcilable dates in the novel:
the other (Monday, 31 July) is contained in Walton's fourth letter to his sister (I:L4:1).
It has been noted, however, that the shift of one day here (to Thursday, May 8) would
reconcile the timeframe, allowing us to date the year of William's death as 1794 and
of Walton's letter as 1797.