A minute or so is usually fine
Unless your riding in sub-freezing temperatures of course, then you'll want to let it warm up a bit, but if not. I wouldn't worry much about this.
The LC version of your BMW boxer motor has considerably tighter tolerances than the air cooled version as it does not have the temp/heat variance as much as an air cooled engine has.
This means, it's more modern and less prone to piston rattle and what not and can be run much sooner than an air cooled engine.
When warming up an engine I'm typically touching the cylinder and ensuring that it's getting hot. After a minute or so of running on LC engines, I feel comfortable.
Occasionally, I'll just start them up, do a few short rev's and take off.