If I'm just casually thinking about something. In other words, it is a subject that does not require too much to come to a conclusion, then I actually think in words. That process can provide a solution almost immediately, to taking several minutes.
If I'm thinking about something that requires a lot of cognitive function, then my mind essentially goes blank. Either I no longer think in words, or the memory of what I was thinking about is not laid down in long term memory until I come to a conclusion. Or if my "sub-consciousness" took over the heavy lifting and my cognitive functions were left out of the loop. I honestly have no idea, but if it is something I am truly concentrating on, I will have no actual memory of the thought process that brought me to a conclusion.
Some of the most confounding things that I have had to think on, I literally slept on it and had a finished thought when I woke up. I have done that several times in my life. Again, not sure if it was just that I needed rest, or if my brain actually worked the problem while asleep and delivered it when I awoke.