I'm a .6 teacher too OP and I think some posters (who are not teachers) are not understanding the issue.
In teaching, we have both 'directed' and 'non-directed' hours. We only get paid for the 'directed' hours'...everything else is done 'because the children' 🤦♀️ and is unpaid. We work many, many 'unpaid' hours.
Our directed time calendar INCLUDES staff meetings, and is directly related to our paid hours. Therefore, a full time member of staff is 'directed' to attend all meetings 'within the directed time calendar'.
As a part time member, we CAN ONLY BE DIRECTED to attend a percentage that equates to our working hours...ie in mine and the OP case, 3 out of every 5. The same is true of INSET days, regardless of what day they fall on, as we are ONLY PAID to attend 3 out of the 5 inset days.
We get a list of termly staff meeting topics at the start of each term, and I negotiate with my head which of these she would prefer me to attend.
I only attend 3 inset days...but again, I negotiate with my head which of these she feels are most important. If she wants me to attend more I get paid to do them, but can also say no if I don't want to.
OP your union will support you with these negotiations if your school are being unreasonable. Please don't be bullied into working even more hours 'for free' than you already are doing.