it appears that there is a fault in the job validation code in backup.pm. The offending code is:
if ($job->{starttime} =~ m/^(\d{1,2}):(\d{1,2})$/) {
($hour, $minute) = (int($1), int($2));
die "hour '$hour' out of range\n" if $hour < 0 || $hour > 23;
die "minute '$minute' out of range\n" if...