rpm -qa --qf '(%{INSTALLTIME:date})%{NAME}\n'
Will yield something like this:
(Mon 20 Feb 2012 01:45:49 PM UTC) libSDL-devel
(Wed 30 Nov 2011 06:24:38 PM UTC) kdebase4-workspace-liboxygenstyle
(Sat 14 Apr 2012 07:27:40 AM UTC) ffmpegthumbnailer
(Wed 30 Nov 2011 06:19:28 PM UTC) ptools
(Thu 05 Jan 2012 07:41:54 AM UTC) NetworkManager
(Fri 11 Nov 2011 12:17:16 AM UTC) xorg-x11-driver-video
(Wed 01 Feb 2012 01:32:00 AM UTC) libmysqlclient_r18
(Wed 30 Nov 2011 09:22:45 PM UTC) libwpg-0_2-2
(Wed 30 Nov 2011 06:21:22 PM UTC) gegl-0_1
(Sun 01 Apr 2012 08:00:55 PM UTC) glibc-locale-32bit
(Wed 30 Nov 2011 06:24:38 PM UTC) kdebase4-workspace-liboxygenstyle
(Sat 14 Apr 2012 07:27:40 AM UTC) ffmpegthumbnailer
(Wed 30 Nov 2011 06:19:28 PM UTC) ptools
(Thu 05 Jan 2012 07:41:54 AM UTC) NetworkManager
(Fri 11 Nov 2011 12:17:16 AM UTC) xorg-x11-driver-video
(Wed 01 Feb 2012 01:32:00 AM UTC) libmysqlclient_r18
(Wed 30 Nov 2011 09:22:45 PM UTC) libwpg-0_2-2
(Wed 30 Nov 2011 06:21:22 PM UTC) gegl-0_1
(Sun 01 Apr 2012 08:00:55 PM UTC) glibc-locale-32bit