I'm remote teaching a #Linux performance and tuning course for some system administrators in Germany.
I share my terminal so the students can see the commands I'm typing for examples and such. When we take a break, I'll give them a time frame, then execute the following script in my terminal:
$ i=$((15*60)); while [[ $i -gt 0 ]]; do clear; echo $i | figlet; sleep 1; i=$(($i-1)); done
This is a large countdown timer in seconds. Screenshot attached with 419 seconds remaining.