How many chats do we get in 3 hours with GPT-4o (Plus members)

ChatGPT
1

I find with GPT-4o it is definitely more than with GPT-4, but I haven’t hit my limit yet. Is there a set number?

If I use up my GPT-4o credits in a 3 hour period, can I use GPT-4? Do those count together or separately?