I regularly get codex to do multi hour tasks with a single prompts I don't think thats a big deal anymore. But you don't want a single agent doing all the work. The root agent needs to delegate the work to sub agents. For example, a sub agent for context gathering, then one for planning, then one (or more) for implementation, then another for review. This way the root agent doesn't use up its context window and it just manages from a bird's eye view. I do have the $200 plan though.

It's going to work the same regardless of how much you pay, but with Plus you'll run into 5h usage limit rather quickly unless your "multi hour task" spends 90% of the time just waiting around for code to compile. Expect to get an hour or two of active work (single-threaded).

If you have any org email, you can get free chatgpt + subscription.