When Jesus reaches the vicinity of Bethany, John states that Lazarus has already been in the tomb four days. The detail is repeated later when Martha warns about opening the grave.
The chronology deliberately removes any impression that Jesus has arrived during an uncertain medical crisis.
Jewish burial normally took place soon after death, often on the same day, because of climate, purity concerns, and customary respect for the dead. Mourning then continued after burial. Later Jewish traditions sometimes discuss the soul lingering near the body for three days, but those later texts should not be treated as the necessary explanation for John's 'four days.'
The Gospel's own purpose is clear enough: Lazarus is dead, buried, and has remained in the tomb for days.
The burial custom makes the four-day notice especially forceful. Jesus is not arriving before burial to revive someone thought dead only moments earlier.
The sign that follows confronts death after the household and community have already entered the normal practices of burial and mourning.