This is awesome! And how cool to be “famous” now. 
Great to have the counter – and the notification of completion.
For me the crucial thing is to have some options for different types of writing. Sometimes, it’s just a matter of needing some help in getting the pump primed, of not dallying in starting to write about something. For those cases, 2 minutes is actually just fine. Sometimes, though, it’s a matter of really forcing myself to stay with something, and then either 5 or 15 minutes seems best. So, if I had to pick one, I’d go with 5 minutes, but 2 and 15 minutes would be great lengths to have.
For the cutoff timer, I’d probably go with 5. I tried 10, but a felt myself getting soft…
The other thing about having a 2 minute timer that it fits well with David Allen’s “2-minute rule” on a task. I could imagine having Obsidian open next to my email app, and then I have to focus on writing (in Obsidian) what I want to say in response to the email. Then: select all, cut, paste into email, and send.