Hey Michelle, I have developed something that might help you with your goal of pacing your breathing. https://breather.school/ is a small web app which plays an animation to which you can sync your breath. The default settings are 5 seconds in, 0 seconds hold, 5 seconds out, which - as you pointed out already - seems to be the sweet spot. But there are other rhythms as well which can be great for meditating etc.
I open the app and put it on a second monitor while I'm working to remind me to breathe properly. But you can also simply put it into the corner of a single screen or use it for dedicated "training sessions." I also know of people who open it on their iPad and put that on their desk.
Let me know what you think and if you have any ideas for how it could be improved!