I call my "timer" a "nagger" and use it via a shell nagme() function. Takes care of certain ADHD traits which were previously causing "refocusing" during unpleasant tasks, like emptying the washing machine (half or less clothes would go to the dryer and half would stay in the washing machine while I'd switch to other task). I learned to only turn off the nagger after completing a task and it works.

It's used not just for time-sensitive tasks but also not to over-engineer stuff during hyperfocus.

    nagme () {
        [ "$#" -ne 2 ] && printf "usage: $0 [in_minutes] [text]\n" && return 1
        printf "sleeping $1 min before telling you to $2\n"
        sleep $(echo $1\*60|bc)
        espeak "$2" > /dev/null 2>&1
        while :
        do
            sleep 30
            echo -n '.'
            espeak "I'm nagging you to $2" > /dev/null 2>&1
        done
    }