I am also on a parent panel, it starts at 9.30am so I just go in to work late on that date - we get the dates for the panel at the beginning of the year so I can organise my work diary so it doesn't clash,. But if it does, I just send my apologies.
I think times of parent panel and the fact that there are no parent "evenings" is just the sort of thing the parent panel is for - the head discusses issues with us the parents and we all give our views from parents point of view e.g new policies, school meal system, new payment system, school trips, communications with school, new initiatives etc.
We are a real mixture, some working full time, some part time, some with one child in reception, some with a child in each year so we all have different views on all sorts of things.
As a working mum, I would be asking that the school considers at least one parent "evening" for working parents!!
Attend the panel when you can and get that down on the agenda!
We obviously don't always get everything as we want it, (we don't all want the same things anyway!) as parents are just one stakeholder within a school and not the most important one, but at least we get consulted and some things.
We can also suggest agenda items and make points via email on specific items if we can't attend.
I imagine the head does not particularly look forward to our meetings but it does help him consider parents views on things and maybe reduces compliants overall - at least his response to complaining parents can be "well we consulted the parent panel and they thought it was a good idea"!!