Hi Anne,
My mom was diagnosed with bulbar onset about 4 months after her voice started slurring. Hers was similar to yours, where there was definitely a noticeable difference in her voice from morning to evening, and I could tell her voice got weaker throughout the day. It was about 6 months after her diagnosis (so about 10 months after the start of slurring) that her speaking was too hard for us to understand, and then she lost it entirely.
I love the idea of taking videos – I wish that I had more of my mom. I really treasure the ones that I was able to get. Also, if you’re up to it, it might be worthwhile to start voice banking now so that you could use your actual voice via a text-to-speak tool down the line.
Feel free to reach out with any questions! I learned a lot taking care of my mom and I’d be happy to give you the nitty gritty on her/our experience, if you think that’d be helpful.