Before listing the constraints of a day, we must define what a day is. A day, for most of us, starts at midnight and ends at midnight. Then the date changes and we are on another day. That’s the easy definition.
Some businesses that need to stay open 24 hours a day 7 days a week will have a different definition of the day. For example, a casino has its peak of activity at midnight which makes things difficult to break down if a planner needs to split the hours when most employees are scheduled. In these cases, the split of the day happens at the lowest point of business in a day. Again in a casino, this would be at 5am or 6am. Hospitals and manufacturing also measure and count schedule constraints against a day that fits standard shifts. This would typically be at the end or the beginning of the night shift. For example, if the night shift is from 11pm to 7am, you either count that shift to be part of the day it starts (making the day be from 7am to 7am) or to the day it ends (making the day be 11pm to 11pm and making one hour of the previous day belong to the day).
Note: try not to make that frontier 2am or 3am. These hours are when time changes occur twice a year in most areas of the world. Having a frontier at 2am will make things confusing when that 2am becomes 3am when daylight savings time kicks in. You’ll feel like an hour has disappeared into oblivion.
Once you’ve established what the day is, you also need to determine how the shift is tied to that day. If your constraint says that employees can work a maximum of 12 hours in a day, how do you handle the shift that overlaps that day frontier? Let’s say that day frontier is midnight and your employee is scheduled for an 8-hour shift starting at 11pm. There is one hour on the day the shift starts and seven hours on the day the shift ends. Therefore, you need to establish the rule on how hours are counted for the employee. In most cases, all hours will be counted towards the day the shift starts, but I’ve even seen businesses determine the day of a shift based on where does the middle of the shift falls. For example, a shift from 7pm to 3am would belong to the day it starts (the middle being 11pm), but a shift from 9pm to 5am would belong to the day it ends (the middle being 1am).
Now that you have established how to count, we can take a look at what to count:
- Minimum hours in a day: Although it may sound like the same constraint as the minimum shift duration, it is quite different. First, it depends on how you count hours in the day. Second, you may have split shifts. A split shift is when an employee works a few hours in the morning and a few hours in the afternoon. Typical employees working split shifts are bus drivers where they work during rush hours. So although you have a minimum duration of 3 hours on a shift, you may have a minimum duration of 6 hours on a day for example. So if you schedule a 3-hour shift, you need to schedule a second one on the same day to respect that daily constraint.
- Maximum hours in a day: For the same reasons, and again depending on how you count your hours, you may have to define a maximum hours per day constraint. This is also different than the maximum shift duration constraint since split shifts may come into play (see above).
- Minimum rest between shifts: This constraint is the most common. How much rest time do I need to give an employee before scheduling them for another shift? This minimum rest is the duration between two shifts where you expect them to go home (this is not the separation time between split shifts). You need to establish a proper value based on the average shift duration you normally schedule and the expected travel/rest time anyone would require before being back and productive. The longer the shift duration is, the longer the minimal rest should be. You may also have different minimum rest values depending on the shift that is worked. For example, after a night shift, you may force a 12- hour rest period instead of the standard 8 hours. The same goes to have a different rest period apply before a shift. If the day shift is particularly busy, you may have a 10-hour rest period before the shift is started to make sure the employees come in rested and productive.
- Maximum number of shifts per day: This constraint will be required depending on how you associate shifts to a day. If you schedule an 8-hour shift starting at 7am and another one for the same day starting at 11pm, you have two shifts starting on the same day with an 8-hour period in between. You have respected the minimum rest rule but the employee would end up being awake for 24 hours in a row basically (not much time to go home eat, sleep and come back). Also for split shifts purposes, you may define how many splits may occur in a day by having a maximum number of shifts per day.
- Shift separation: Shift separation is for split shifts. As explained above, a split shift is sometimes required by the business simply because of the workload profile that has multiple peaks in the same day. Although these are good for the business, they are usually not very popular with employees. With this type of shift, you need a reasonable minimum and maximum duration between the two parts of the shift. The minimum value is driven by the business. If the minimum is too low, then the separation becomes one long break that the employer would have to pay. The maximum value is driven by employees. If the maximum is too high, then employees are away from home for a very long duration. Thus, a reasonable balance is required. Some employers pay up to 25% the duration of the shift separation in order to be able to schedule them and not end up with outright refusals from employees. This all depends on the business requirements and demographics that are involved.