I’ll echo the sentiment that if you are part time, and especially hourly, you have the right to protect those boundaries with 100% consistency. I’ve shamelessly turned down a lot of meetings and tasks because “I have a hard stop at 3” and “I’m already at my hours for the week”.
This is something I really need to work on. My challenge is that I'm a team lead and the rest of my team is full time so I always feel I need to check and respond to emails on off days. Also before my leave my director was always scheduling meetings for 3pm when my hours are 7-3.
The problem is that I'm in a full time position but was allowed to switch to part time for a while because I have young kids. They've asked me several times when I plan to return full time and I feel a lot of pressure to do extra work so that they don't force me to work full time.
How formal is your part time agreement? To ease some of the pressure it might be best to communicate both your and your employer's expectations on how long the part time work would continue. They may genuinely be curious but you could be interpreting it as pressure to go back to full time. This could also back fire, so the other approach is to shrug it off.
I am a team lead / project manager that was full time but now work 3/4 time (8-3). I have a couple of tips and if you want more details on how I manage my time feel free to PM me.
First, on meetings outside of my schedule, I assume that nobody knows my schedule (even though I have office hours set in outlook) so when they schedule something outside of it i respond with a no but with a note letting them know it's outside my work schedule and am open to meetings another day / time. There's some nuance, but that's how I've approached saying "no" professionally without making it personal.
Second, it sounds like you may be working full time hours with the off hours emails and discussions but taking part time pay. You need to remind yourself you chose to go part time and were approved by the company to do so, and with that comes a part time workload.
For my projects i keep a team project schedule with my hours, and if new things come up that require my time i say I'm sorry I can't I'm full on workload for the next X weeks/months depending on the commitment, or if absolutely critical needed my engagement on these other projects can stop but here are the impacts.
I do however have supportive management of getting me to a part time workload and I'm almost there. I've been transitioning for a few months and i can almost taste the sweet relief of an actual part time workload. I did agree to the transition. I should also caveat with I'm a government employee so I have a bit more protection.
The biggest thing though for me is how much easier for me to say "no" to extra work after a while. The last few weeks I've also been able to keep from checking emails a couple times a week in the evenings, but it will be there in the morning to deal with whether I look at it or not.
Regardless of who you work for, learning to say no professionally and having boundaries is a very, very healthy thing. It will drive your burnout further if you don't.