I was in a similar situation, where I had phys 1L03 in second term and I wanted to switch it to phys 1B03. In November, I went to go see an academic advisor, who first tried to convince me I'd be better off in 1L03, then when I insisted I'm not physics challenged and would much rather take 1B03 so I don't have to in 2nd year, she wouldn't open up a spot for me, and instead told me to wait until December/January, because people would be taking 1L03 first term and fail it, and thus have to drop 1B03 second term. I ended up getting lucky on SOLAR in early December, at around 3am