I understand where you're coming from. I (like the PPs), don't think the exact day is as important as marking the event around that time. To my parents and my ILs, though, that DAY is important.
We live within a 25 minute drive from both families, and they are within 15 minutes of each other.
For six years after college, I was working on my professional credentials and always had exams at the end of May so I skipped Mother's Day to study, and my mom understood the stress and let me put off Mothers' Day for a week. I am now reminded of that every. single. year. (It's been 11 years).
When I became a mom just over 9 years ago, I wanted to make a tradition of doing the Susan G Komen Race for the Cure for breast cancer. It was on Mother's Day in the morning. Both my mom and my MIL were not at all pleased and I gave up the race (actually, we did the 3-mile walk like most of the particpants). My mom and MIL are normally very reasonable, and this just wasn't the hill I was going to die on so I figured I'd work it into Mother's Day sometime in the future. We've only done it twice so far.
One thing I changed though, was I reached an agreement with my husband: Mother's Day was with my family (following the female family lines) and Father's Day was with his family (following the male family lines). Both families had to compromise a bit but it seems fair enough, and it eliminated half of the stress.Side question: is it Mother's Day or Mothers' Day?