I don't agree so much with point 2, but I do think that it's smart to figure out what people actually need to be in the office for and plan around that, rather than assuming some kind of window. Maybe the lunch meeting at one startup is the 4pm at another.
1/ Don't add process until it's necessary. Why have office hours, a vacation policy, or any rule that requires employees to expend mental capital on superfluous issues?
2/ If you're to the point when that process is necessary, you probably hired the wrong people (especially in a startup).