Start and End Times for Both Regular and Overtime Hours from General Hours Worked?

Hi All,

Our client is a medical professional who essentially got screwed (and VERY overworked) by his employer. I need to know how to draw out overtime start and end times, as well as the regular hour start and end times, from the total times worked for each day he recorded his general hours. Basically pay schedule is tiered like so:

(A) Weekday regular hours: 7am-3pm (8 hr total)
(B) Weekdays on call [overtime hours]: 3pm-7am (16 hr total)
(C) Some weekends on call [overtime hours]: 7am (Sat.) - 7am (Mon.)

He is also entitled to payment on the weekends as set out in (C), but I can handle that manually if need be. I just really need help setting up a formula to parse out start and end times of (A) and (B) from the generalized hours he gave us in the spreadsheet.

Very much obliged,

Frustrated Law Clerk