I have taken the following information and references from this article, so I do not claim the hard work for myself!
The corpse of Isabel, Duchess of Clarence (†1476) was brought to Tewkesbury Abbey in Gloucestershire. A monastic chronicle describes how it arrived there on 4 January 1477 and remained in the middle of the abbey choir for thirty-five days, during which period daily prayers were said for the Duchess’ soul.
Although her body would not have been exposed to view (the chronicle states it was ‘subtus le herse’, under the hearse), it would not have gone unnoticed by the monks, who needed only to look to another monument in the middle of choir, the cadaver effigy of Isabella’s grandmother, Isabel Countess of Warwick (†1439), for a vivid depiction of the decomposition of the Duchess’ concealed corpse.
I must confess that I’m a little squeamish for these medieval ideas. John of Gaunt instructed in his will that his body was to remain unburied for forty days:-
“ . . . And wherever I die I will and devise that after my passing my body remain above ground uninterred for forty days, and I charge my executors that within those forty days no interment [Lincoln MS: embalming] of my body shall be done nor feigned, privately nor publicly . . . ”
 Another close parallel is the will of Joan Beauchamp, Baroness Bergavenny (†1435), which stipulates that ‘my body be kept unburyed in þe place where it happeneth me to dye unto the tyme my maigne be clethed in blak, my hers, my chare and other convenable purviaunce made and þanne to be caried unto þe place of my buryeng’. Quoted in King, ‘Contexts of the Cadaver Tomb’, vol. 1, p. 229.
 ‘The Founder’s Book of Tewkesbury Abbey’, in William Dugdale (ed.), Monasticon Anglicanum, rev. edn, vol. 2 (London, 1819), p. 64. See also Julian Luxford, ‘The Founder’s Book’, in Richard K. Morris and Ron Shoesmith (eds), Tewkesbury Abbey. History, Art, Architecture (Logaston, Heref.: Logaston Press, 2003), p. 60.
 ‘Founder’s Book’, p. 64.
 The cadaver tomb has not survived, but is described in Isabel’s will. The Fifty Earliest English Wills in the Court of Probate, London, ed. Fredrick J. Furnivall (London, 1882), pp. 116-17. See also Phillip Lindley, ‘The Later Medieval Monuments and Chantry Chapels’, in Morris and Shoesmith, Tewkesbury Abbey, p. 176; Julian Luxford, The Art and Architecture of English Benedictine Monasteries, 1300–1540: A Patronage History (Woodbridge: Boydell, 2005), p. 173.
For a lot of pictures of the tombs of Tewkesbury Abbey, go to http://www.churchmonumentsgazetteer.co.uk/Gloucester-Tewkesbury.html from which I have taken the illustration above of the Clarence Vault entrance, where both Isabel and George of Clarence are now without grand tombs, but lie beneath the floor behind the altar. The picture below comes from the same site.
I’m sorry, but my feeble modern self finds this just a little too much. 35-40 days before you’re buried? OK, but not without embalming or fridges? Sorry. I think I’ll stay in 21st-century England after all . . .