Mainly /goal mode of complex project/prompts. Example: https://doxygen.rpnx.net/cortado/ was nearly a one-shot for GPT 5.6 sol and took well over 1 hour for the first prompt before finishing.

But anything to do with compiler development tends to leave the AI spinning its wheels for quite a while.

Edit: Checked the time on that one, I confused it with Compress taking 3+ hours for 1 prompt and another couple of hours each for the next few prompts... Cortado was still well over 1 hour for the initial prompt though...