Preparing a lecture takes a heck of a long time. The lectures I had already done twice before were already sort of OK, but still needed some tweaking; some had been too long and needed pruning, and some bits had gone outdated. That needed fixing. But it was more work to sort out the lectures I had not done before.
I did not start from scratch; I inherited Paul's lectures, and he had inherited them from James. And I know James' presentations; they only make sense when you're James. He has a monumental amount of knowledge in his head, and he can spin that into amazing stories, guided by the merest hints from PowerPoint. But for people who have a different head, these hints might not be enough. Updating his lectures which often are full of graphs and images without any explanation,and often in grainy, nineties (or worse) quality, is a lot of work! But it also is fun. I like knowledge! I love reading up on stuff! I love looking at a slide, thinking first that all is well but then thinking "hang on, but why is this or that the case?", then looking it up, and then having filled yet another void in my knowledge. Lovely!
With it being so much work, and it having become more do to being in the field the entire Tuesday (which meant I had to move three lectures in the already busy rest of the week, and the following ones) I needed to work over the weekend. Luckily I could do a lot at home; on Saturday, I didn't go to the office. I had brought all my presentations with me on Friday. Nice to work in a heated house, with the kettle nearby! Nicer than in a cold office in a dark empty building that you have to entirely traverse to get to boiling water. Although on Sunday, I went in anyway; much easier for looking up references, and for swapping between windows as I have two screens. Luckily I could use my office mate's electric heater!
One thing that saved me a lot of time was that one of the lectures I had to prepare was a fourth year lecture on Milankovitch forcing, and I had already read up on that a lot in order to explain it to A-level students. And that sounds very different, but it isn't really, as I had had a lot of these "hang on" moments then, and they have been weeded out now. I went back to my notes from that time, and got reminded of a lot of interesting stuff I can put in! I knew it would come in handy sooner or later!