Back to OP ...
Your posts, all of which I have read, don't add up.
I appreciate that some people have such senior jobs that working very long hours, including early starts / late evenings, is inevitable.
That doesn't sound like your situation though, in terms of your anxiety over not being available for the 5 p.m. meetings, and not having the kind of disposable income that means you can throw money at the problem (again, most people can't!)
The idea that you have contracted hours but still, don't have set working hours makes no sense. Of course you may choose or have to work late, but a standard contract will provide the expected working hours, though may caveat it with 'and other times according to business need' or similar.
From the level of management you appear to be at, you should be able to do two things
- Have a clear understanding of what your scheduled working hours are e.g. 9 - 5 with a 30 minute break (for example) even if practically speaking you on occasion work longer
- Clearly state your lack of availability, as others have suggested, after a certain time, barring extreme/occasional need.
Finally, routinely working after hours when your children are in bed isn't sustainable. You will do more and more work, that's all there is to it - and if you stop, they'll wonder why you aren't still churning out work as needed.
There is a balance - I work in a middle management position in a university; I manage a very busy team, I spend a lot of time in meetings. I choose to occasionally do some work in the evenings / weekends - that ensures research / project work or projects I'm particularly focused on for myself, get done. But the idea I would be expected to work a full day, then start again at 7.30 is not reasonable or something that should happen. You really need to address this.