(And the argument for including a short video on your website in the first place is compelling. Many people are visual learners, and the ability to remember information, faces and impressions is also primarily visually-based.)
The theory for specifically advertising a short video comes from years ago when grocery stores used to place popular items at the end of long aisles, which forced consumers to commit to walking down them—and past lots of other potential purchases, of course. The strategy eventually backfired as consumers who saw long aisles began carefully reading the aisle signs at the front of the store before committing to heading down a long aisle, thereby making their shopping trips much more efficient and shorter in duration. Consumers basically stopped consenting to having their time engineered for them through the store’s bald attempt to separate them from their cash through impulse purchases.
So, grocery stores resolved this silent consumer revolt by opening up aisles to other aisles—creating a more divergent traffic pattern—so that consumers could see that, halfway down the aisle, they could jump sideways to another aisle. Grocery stores gave up precious shelf space to create these intersections between aisles, and consumers regained some of their freedom while offering up more shopping time. The compromise worked.
The same strategy works for inspectors who have online promotional videos on their websites, too. Keep your visitors on your site for as long as possible by giving them useful information, but let them know that you respect their time by presenting that information sensibly and in a user-friendly format, which includes videos. Advertising that your video is short lets them know that their valuable time will be well spent.