This was a really interesting IA for me to write, especially because the topic I picked intersected with the theme I was exploring for another IB class at the time. I picked a titration-based lab, but because of all, it entailed I ended up spending 7ish hours in the classroom getting it done. However, I would 100% recommend trying to get your experimentation done in one go. At the end of the Saturday I was exhausted, but knowing that all I had to do was write the rest of my IA was incredibly relieving. One of the things I would recommend in writing out your procedure is to try to explain everything -- even if you don't think it needs to be written down.