Iris has feature which reminds you to take a breaks from time to time. Here you can set the duration of the work in this case 30 min and the duration of the rest, in this case 5 min.
You can force the rest with the Have a rest now button or with the shortcut Ctrl+Alt+Enter
There are several places which show the remaining work. One is the tray icon, the other is the upper right corner of Iris. You will also get notification for incomming break and postpone window 10 sec before the break.
You can read for about the break reminding from the dedicated article.
When I was working in office I used intervals of 30/5 minutes and this is the Iris default, but this days I generally don’t need to take breaks, because my eyes feels good thanks to the many other good features for eye health.
You can stop the work timer from the tray menu if you want.