I think Yeshivas in the US fall into 3 basic formats:
- Modern Style day schools - (regardless of whether they're separate or co-ed) that intersperse Judaic and Secular studies throughout the day. So if there are two classes per grade, one class starts the day with Judaics, the other would start the day with Secular and then they switch midway through the day. There are many variations on this theme, but for the most part both secular and judaics teachers/rebbiem are full-time staff of the school. (for clarity, everyone starts the day with tefila, and then splits off). School is M-F, and Judaics and Secular are taught 5 days a week - even though Friday is a shorter day (9-1:30 vs 9-4:00)
- Yeshivish with serious secular studies - the morning hours are devoted to Judaic studies (9-1 or 2), and secular studies are taught in the afternoon. (2-4:30, 3-5:30) - there is a practical reason for this. The school hires secular studies teachers who teach in public or other private schools in the morning, and are looking to make some extra $$. The teacher benefits because they have a side job, the school benefits because they get qualified teachers at a lower cost. In this environment Judaics are taught either 5 or 6 days a week, and secular M-F (Sundays typically had a full judaics schedule, vs Fridays that had an abridged schedule)
- Chasidish/yeshivish without serious secular studies - I don't know much about the breakdown or how this is approached, but I do know that a lot of my friends who switched from those environments did so because the secular education wasn't taught seriously.