The MAXIMUM viability time for a liver is about 12 hours - maybe a little longer if you are very lucky. (Kidneys can be kept for considerably longer so are less urgent). Typically storage times for livers are about 7 hours. Now do the sums from the time that ( to use a sad euphemism ) a donor becomes available through to having the recipient in theatre receiving the organ and you will see that any delay - especially of at least an hour - could cause immense problems.