By all means, do a pomodoro, but don't use a ticking, vibrating noisy kitchen clock.
On a side note, I used to work in a small software startup where I was the only female. I was on my period at the time and also wanted to fix my hair, so I just brought my purse with me. I crossed paths with one of my co-workers on the way to the bathroom and he asked "Are you leaving?" I told him I was just going to the bathroom. He said "Why are you bringing your purse?"
I just looked him straight in the eyes, smiled, shook my head slightly, and said "Dan, never ask a woman why she's taking her purse to the bathroom." I'm pretty sure he walked away more embarrassed than I was ;)
But yeah, I'd rather do THAT once in a while than keep a freaking timer on my desk.
I also don't believe that everybody would jump on this bandwagon and totally share the sentiment expressed in sibling comment by maccard.
Most people can easily, effortlessly, sit much longer than that before they start to feel stiff or restless and so naturally take a break. It is very easy to unintentionally end up sitting too long.
It almost feels like you are doing the exact kind of post-rationalization I said is an unhealthy thing to do :)
Nothing beats coming out of a 3 hour programming blur when you realize you haven't eaten anything and have to pee real bad... but you re-wrote that entire module that everyone hates and thought would take weeks to fix. MIC DROP
But then they will notice that your break did not coincide with the timer, and (depending on the floor plan of the open office), that you did not head for a walk, but straight for the toilets.
Get one of these kitchen timers [1].
Set it to about 25 minutes.
When it goes off get up from your desk and spend a few minutes walking around the office.
Return to your desk, reset the timer, and go to prior step.
When you wish to visit the bathroom do so on one of your strolls around the office.
Coworkers will ask what you are doing (this is one of the reasons to use a physical timer instead of something running on your computer...it will be noticeable). Here are three reasonable explanations for why you go on a stroll around the office every 25 minutes or so.
1. It is unhealthy to sit for extended periods. If you get up and move around every 25 or 30 minutes or so most of the bad effects of sitting can be eliminated or greatly reduced [2].
2. When solving problems it is best to have a mix of "focused mode" and "diffuse mode" thinking. Get into focused mode and then when the timer goes off you can take a break and let diffuse mode take over. That walk around the office is perfect for some diffuse mode thinking. There is much more about this in the "Learning How To Learn" course available at Coursera.
3. There is a time management technique called the Pomodoro Technique [3] built around breaking tasks into 25 minute chunks paced using a timer.
Once people see you doing this I'd not be surprised if several other coworkers start doing the same. Reason #1 alone will get a lot of people.
Once several people are doing this no one will have any idea how often you visit the bathroom (well, except for those people whose can see the bathroom from their desks). And as a side effect you'll have better health and productivity.
[1] https://www.amazon.com/60-Minute-Kitcher-Timer-Tomato/dp/B00...
[2] http://ergo.human.cornell.edu/cuesitstand.html
[3] https://en.wikipedia.org/wiki/Pomodoro_Technique