It's imposible keep an erection for so long ... much less without a constant and vigorous movement (๑•ㅂ•)و✧
Without any rhytmic movement, the penis will flaccid and will come out by itself... So, if one erection is maintained for a long time, vasoconstriction will impede blood supply, and may cause necrosis... In extreme cases it would be necessary to amputate.
Yasashii Pantsu no Nugasekata