It would be nice to add an option to the nightly cron job, enabled
with a setting in /etc/sysconfig/yum, to only download the new
packages but not install them. (Ie. Add the --download-only flag.) A
user can then perform the actual update interactively, without waiting
for the download.
See bug 125898 for other enhancements requested for the cron script.
It probably makes sense to implement them all at once.
the cron job is a text file and marked as a config file.
you can just add --download-only to it yourself.