Job time periods in VSys Live are designed to make it easier for volunteers to find jobs online. Rather than specifying explicit times of day, they can select "Mornings", "Evenings", etc. VSys Live time periods can be calculated automatically for each job opening based on the job opening's (slot's) start time or they can be explicitly assigned to individual openings.
For a given time period, if Manually assign to each slot is checked then this time period won't be used for searching unless it's explicitly assigned to one or more slots. Otherwise the date and time ranges are used when VSys Live searches for a job by time period. If a slot meets the criteria for the job time period based on its date and time, then it's considered to be happening during that time period and will be found when a volunteer searches by that time period.
It's okay for job time periods to overlap each other: a job opening is considered to be part of all of the job time periods whose criteria match the slot's date and time.