Hi Nira,
I'm not a manager, but I'm a RN with lead nurse experience. I worked in an adult PC clinic for a large ambulatory care clinic affiliated with a hospital that was open M-F 8am to 630pm (extended hours from 4pm-630pm). This might not be relevant to the changes being made in your clinic but to give you some background, initially, they had the nursing staff working 4x10hr shifts; everyone worked full-time hours. Staff were assigned a regular day off (RDO) of either every Monday or every Friday. Most of my fellow coworkers liked this option because it gave a RDO to tend to errands and prevented some unnecessary callouts.
Upper management restructured our clinics. The providers and 2 supervising nurses worked 10 hrs, but all nursing staff were changed to 8 hour staggering shifts: 8am-430pm (most staff) or 10am-630pm (3 staff to assist the 3-4 providers in the after hours clinic). The 3 staff working in our after hours clinic were worked to the bone; they had to focus only on the patients in the clinic and had no time for any other task (ie patient messages, outreach, etc). Walk-ins were not accepted after 430pm, which is when most of the other nursing staff left. Our nursing staff are union represented, so based off the union contract management asked nursing staff for volunteers to change their shift. If there weren't enough volunteers or people willing to work a certain shift, then to meet the staffing needs of the clinic they would have to follow the seniority list.
For vacations, only one RN, LVN, or MA was granted vacation at a time (ie if 1 RN had a week off, then another RN could not be granted that same week off).
For unexpected calls off of the staff working the after/extended hours, they would either ask someone to do overtime, or they would have the supervising RNs work the clinic (since the supervising RNs worked 10 hrs and because of the budget cuts).