Absolutely not unthinkable! We're paid for exactly that in research, for example.
It's terrifying to hear that 5 hours of focused thinking is considered crazy. I can understand a budget battle if it's 5 months, but 5 hours?! Everyone, in every profession (or none), would be better off mentally if they "wasted" 5 hours thinking about something every now and then!
I completely agree with you, but being "better off mentally" is really not valued very highly today.
Fast, visible progress and delivery is the melody.
If 5 hours of thinking time to solve a problem is unthinkable to some people does that mean they have some form of Attention Deficit Disorder, be it a natural thing or introduced by an over-dependence on LLMs? Like stopping for an hour to think through a problem is unfathomable and instead they would rather hit small dopamine spikes every few minutes from talking to a chatbot?