One nice benefit of doing the number first in the url is that the second time you set a timer you can just type a single number and url autocomplete will fill in the rest for you.
The URL feature would be really useful, especially if you put the UNIX epoch time in the url. This way you can send the timer to other people/devices, and you can also close the tab by mistake and have the countdown pick up exactly where it should.
One nice benefit of doing the number first in the url is that the second time you set a timer you can just type a single number and url autocomplete will fill in the rest for you.