Managing timezones can be tricky. Sometimes an in-person call is the best option to advance the work quickly, but multiple timezones make it either impossible, or mean that someone has to be up late or early to attend. The workaround is to record a video message, watch later and comment async. This generally works well – most of the time it's actually a great option, but in some situations an in-person discussion would be more efficient. On balance though the benefits of working remotely far outweigh any minor inconveniences like managing timezones.