It depends on the industry but if the work is not time sensitive, I'd tell employees to start whenever, and finish 8 hours (or the appropriate shift length for the type of work) after that. I'd plot the average start and end times in a chart and I'd schedule any required team meetings to catch the largest overlap of employees (within reason, aiming to keep that overlap between 8am-6pm, unless we're all somehow on night shift)

I have a circadian rhythm disorder and shift start and end times not lining up with my natural sleep pattern is honestly the worst part of working. There's got to be a better way to do it. Humans aren't designed to start and stop work based on a clock, but some of us also don't work with the sun.