And you agree that standard office hours exist for some people but not for you? So the people who should do standard hours are the ones who might inconvenience you if they don't, am I right?
that's your interpretation, that's not what I said at all.
Standards hours, or at least "known" hours are needed for obvious reasons.
People know the office is officially opened and manned between 8 and 8. If they chose to book a meeting there at 10pm, they can't complain there's no one to greet and bring coffee to the client or to take their minutes. No one is stopping them from having a 10pm meeting though, it happens a lot with someone from another time zone.
If someone is only available between 10pm and 5am and no client is happy about that (reasonably) then we have a problem. If you want a report on your desk at 8am Friday, you won't know or care if it was done at 3pm on Thursday or 2am on Wednesday.
which already does cut down her availability to be contacted, so why cut it down further by letting her go off to yoga between 9 and 5 and do her work when everyone else has logged off instead? It just compounds the problem.
Because unless Brenda is your PA, Brenda doesn't have to be available FOR YOU. Send her an email, block her time, don't expect her to wait around in case you need an impromptu chit-chat.
Brenda is professional enough not to book her yoga session when there's an urgent last-minute meeting. That's where it comes down to.
You just want people to match your own schedule, if you have no flexibility, that's your problem, not a reason to penalise the entire office.