For whatever reason, anacron is set to run its daily jobs at 7:30 in the morning:
# /etc/cron.d/anacron: crontab entries for the anacron package SHELL=/bin/sh PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin 30 7 * * * root start -q anacron || :
The first time I encountered that was when I was working at that time of day and noticed the sluggishness of my machine. It seemed that locate was the heavyweight process, so I changed anacron to run at 4:30 a.m, modifying the last line in the file:
30 4 * * * root start -q anacron || :
Jeff Pace's Blog 