I cannot do slow. It is either burn the candle at both ends, or do nothing at all.
I am using LLMs this time as well, but I spent close to 400 hours over a period of 6-7 weeks on my project before I put it to the side temporarily (got bored once the thinking part was done). About 300 of those were spent on iterating over the language and VM specs and eliminating all ambiguities and needless features. The remaining 100 were used to produce the code --- the VM, the assembler and the compiler --- and to repeated rewrite it to conform to my way of doing things.
LLMs have let me become extremely choosy about which code I am willing to keep.