We have all been there where you are supposed to work on that boring but critical bug for the project, where a few other team members are waiting, but you end up booking a domain, building a landing page, and launching a waiting list. By dinner, as you are talking to potential alpha users in your community and start spreading the word, you realize you have not touched that bug.
Anyway, I like timers; the only complication in my Watch is a timer.[2] At my desk, I use a physical hourglass regularly. The physical hourglass helps me not be constrained by the Pomodoro-ish restrictions and work past the finish line.
For distractions (that seem important and sometimes are) while I'm on a specific task, I usually have my handy notebook, and I write them down quickly with a pen so I can return to them later. That helps me prevent launching ideas into landing pages.
Once you are good with a process/pattern, whatever tool you build/buy/use, as a timer in this case, helps your focus on your current situation.