Here is a story. Some friends and I just agreed to meet for coffee tomorrow at 8am. Even if one of us is running a bit early or a bit late, I expect that we'll all show up to the coffee shop right around 8am central time. This is a reasonable assumption. We all live in Chicago and people who live in Chicago tend to talk about time from the perspective of the Central (CST or CDT) time zone.
Here is another story. I scheduled a phone call with a prospective client over email. We agreed to talk at 9am. However, when I called this person at 9am, they seemed a bit caught off guard. And for good reason, from their perspective it was 7am. I thought we were talking 9am CST and they thought we were talking 9am PST. Two hours is quite a difference, especially at 7am PST.
I'll take the blame here. I suggested a time without including the time zone that I was thinking. And I'm kinda surprised I did. I nearly always include my time zone when emailing or messaging about times. This time I made an assumption and I came up quite wrong.
I'm taking this opportunity to remind myself, and you, to always include time zones.
We can take this a step further by proactively communicating about a number of expectations and assumptions we have around time. From the start, we should lay out what time zone we are working from and inquire the same from everyone else. We should also talk about availability. Instead of assuming everyone operates the same between 9 and 5, find out if there are times of day and days of the week that work best for each person. As a bonus, be clear about how much time you are asking of a person in a call. If you want to talk for 30 minutes, be explicit about it ahead of time and then stick to it.
Once you have these things figured out, you can use a tool like Every Time Zone to find time slots that make sense for everyone.
Time is relative, make sure everyone is talking about the same thing.