Hours of Overlap define the minimum number of hours where team members are available to each other for collaborative work.
The following example is adapted from our book, From Chaos to Successfully Distributed Agile Teams. You can find the complete example in Chapter 8, Building Respect With Working Agreements.
In this example, the team is distributed across four cities and three time zones. Raleigh and Boston are in the US Eastern Time Zone (UTC-5). London is UTC and Berlin is UTC+1. Each of the team members chose different times to come into the office, take a lunch break and leave the office based on personal preference, family constraints and commuter constraints. Actually, Gerrit might just be a nice guy or a night owl as he has adjusted his work times to have more overlap with his colleagues.
With this arrangement, this team completely overlaps in hours for two hours out of each workday (shown by the 100% in the “Overlap Probable” row). That doesn't mean the team cannot collaborate more. The other columns showing 92% and 83% overlap indicate the team may still be able to have ad hoc reviews or co-creation sessions. They just may not be able to get the entire team together outside their two hours of overlap.
Later, Jane in the Boston office would like to be in better shape. She tried different activities and realizes that her best time for exercise in two hours in the middle of her day. She doesn't want to impact the team's collaboration time, but she knows she feels better after working out and can help the team more being fit.
After a discussion with the team, Jane shifts her Tuesday and Thursday hours as shown below. It impacts only one hour of the teams collaboration time and the team notices the overall improvement in their work. Now more of them might be considering a regular exercise routine.
Two hours of overlap may not be sufficient for many teams. It seems to work for Jane's team. It's best to have a discussion with your team mates and discuss how they may adjust their hours to maximize the hours of overlap without putting a strain on their personal life. If shifting hours is not sustainable and the team cannot achieve at least four hours of overlap, you might consider other changes.