However, I do find long hours may result out of necessity for the sheer work involved as well. Especially in the earlier days of a company, you compensate for an initial lack of resources and staff by performing multiple roles.
On the business side, you could easily see your mornings taken up by customer calls (especially if you have an international market), the afternoons spent on ad campaigns and marketing content, the late afternoons on general office management. In the evenings when there's less client interaction, I would spend time on product feedback, some data analysis and metrics reporting for the day/week's past. This could easily extend to a 60-80 hour work week, and I would consider fairly typical of early startups.
As you grow there's less need for sure to work so long, as the company grows and responsibilities become more focused. But overall, I think there are circumstances where a 60-80 hr workweeks are necessary, and not necessarily an indication of a problem.