Good on you for using LM products. They are indeed superb.
Engine warm-up does not literally mean idling engine till it feels warm to touch.
The idling time before revving or riding a bike or driving away in a car is to ensure that the engine oil circulates to all parts of the engine, including head etc to ensure optimal lubrication and hence protection against direct metal to metal contact.
This is also necessary as the first start in a day, it a cold start as commonly known, is the time when most engine wear and tear occurs.
For further ease of understanding, a 5W oil takes about 8 seconds to run through the whole engine, a 10W oil will take approximately 28 secs , and a 20W oil will take about 56+ secs to lubricate the engine.
From the above reasoning, allow at least a minute of idle b4 driving off on a 20W oil.