Figuring out what on earth slows my machine down every afternoon, I found that we run cron.daily at the most unreasonable of times: At 14:40.

From /usr/lib/cron/run-crons:

    ...
    test -e $SPOOL/$BASE && {
        case $BASE in
          cron.hourly)  TIME="-cmin  +60 -or -cmin  60" ;;
          cron.daily)   TIME="-cmin +1440 -or -cmin 1440"  ;;
          ...

I don't mind those cron jobs running in the middle of the night when I am away from my computer. Of course when the machine does not run at that time, there must be a fallback time - but running it at 14:40 every day for everybody does not make sense.

Please move it to, say, 3:00 in the night or some other time then the machine is idle anyway.