Quando Beatrix acorda, é noite. Você entende porque tudo é escuro. Quando vemos a cena de Beatrix deitada na cama antes do mosquito a acordar, a câmera mostra a sala com um movimento circular e você pode ver claramente a janela sendo escura, a única luz vem das lâmpadas acima das camas.
Uma captura de tela da janela
Isso significa que a maioria do pessoal do hospital está dormindo e que somente aqueles que têm um turno noturno estarão lá no hospital, sendo um deles Buck .
No Kill Bill: Vol. 1 FAQ no imdb, existe uma pergunta que diz " Devemos realmente acreditar que ela pode ficar no caminhão de um cara morto por 13 horas sem que os policiais a encontrem? "
E a resposta confirma o que eu disse, também adicionando outras teorias (adicionei os números 1 e 2) e repetindo o que o VoT disse em sua resposta (ênfase minha):
No, just like we are not supposed to believe that arterial spray is that insane and that a very, very old Chinese man can stand on the tip of an outstretched sword (as happens in vol. 2). The film generally does not take a hard, realistic tone. It's possible that it could have been near the beginning of Buck's eight hour (or possibly longer) shift when The Bride took him out. Perhaps the next nurse coming in decided not to check on them for a while because s/he had other things to do, and no one found the bloody mess in the room for over thirteen hours. They were in the coma ward, where nurses possibly didn't check on the patients that often. By the time he was found, with all the usual shock of the discovery of a double homicide, it's entirely possible they didn't get around to checking his truck by the time the Bride left. (1) Not to mention, if they did check for his truck they would see that it was still there, and possibly wouldn't check inside. Seeing as how the truck wasn't stolen, they may not have found it necessary to check it. (2) The Bride also takes the keys to Buck's truck, and without those for identification, no one else might have known which car belonged to Buck.