I worked for an organization where people had one flex day off every two weeks. In practice, it made Tue-Thur the only days for collaboration as it was otherwise normal for someone to be out of the office. It worked because it was government with long project cycles. It would not work for my current company. It would cause issues with clients and project speed.
Seriously.
Especially when you run 24/7.
Then you know it's really bad when a 24/7 operation "rises" to a challenge by calling all hands on deck. And at the same time battle stations because they don't even know the difference.
Collaboration is often limited by the pace of a human interaction: a design review, a question about some code etc. The only way to not have this speed limit is to remove all such interactions which is very difficult (and probably not desirable either). If I worked on off dates and my colleagues on even dates, the shortest time for me to get a code review would be 24h! Most communication can (and often should) be async, but there is a difference between a 10 minute turnaround and a day. Also, if something is very urgent one should be able to get hold of someone e.g give them a call. Developers hate being interrupted, for good reason, but that doesn’t mean developers should never expect to be interrupted.
I think a shorter and flexible workweek is a good idea but having time zone overlap or “required work days” to maximize overlapping work time is probably required in most cases.
Consistency is good.
That's much different than a pet project that's being given away for free.
Also remember that opens source includes things like the Linux kernel. That "pet" project underpins almost all software that the hypothetical corporate uses and makes, and does it without the meetings and the deadlines.
And if we are talking about some of the most important software projects, approx. zero of them are run by hobbyists. Some niche aplications - sure. But not the most important pieces.
(Disclosure: for the last few years I employ 4-8 people to work on GNU GPL licensed products, so I know a thing or two about how it works)
I’ve also developed and led teams that developed many OSS projects and very successful consumer applications. Not once did I micromanage my team’s working hours. They make their own schedules as people know best when they can produce good output.
As for 'micromanaging working hours', it's not a question of micromanagement, but of communication. It is far easier for everyone to work in the same rythm, knowing that you aren't distracting a person you need to contact from his private life.
That’s not flex time at all, that’s a fixed schedule where everyone has either even or odd Fridays off.
If your coverage plan relies on the customer knowing who to call when, your problem isn’t flex time.