And if you have jot, but not Perl, like on a bare FreeBSD install:
0 */8 * * * sleep "$(jot -r 1 0 599)" && ~/.config/jobs/fetch-tcl-logs 0 */8 * * * sleep "$(jot -r 1 0 599)" && ~/.config/jobs/fetch-tcl-logs sleep $((RANDOM % 600)) && fetch-tcl-logs