Depends on the industry / multiple / employees.

You want at least a year where you're systemising the owner out of the business without filling their shoes.

You'd also want some kind of break clause so you can back out if it turns out the business can’t run without the owner, or if the team won’t adapt and can’t be replaced.

Depends on the industry and your experience plus your access to capital. Sorry for the non-answer

Usually... buying proven technology, and marketing lead lists is still a gamble. However, the other YC posters are correct in the "never make what you can buy" advice... if and only if there is still mileage in the product life-cycle.

In general, there are a lot of serious rules around energy and fuel industries. Rockwell and Kongsberg technology still dominate for some very practical reasons. Seeing a few small firms fail hard in the area, I would still call it a fools errand for those looking at low hanging fruit. =3

Buy then build