would it be possible to survive 4+ hours a day in an indoor work environment with a mask on?

I worked a job where I was there for up to 10 hours a day and I endured it. One of the things I did was carry several masks with me and switched them out periodically.

Easily 

No you won't suffocate

Sure--surgeons do it all the time.  The KN95 cuts oxygen about 20%, but a person can live and function with the remaining 80%, even though it would be uncomfortable.

Doctors and nurses have done that every damned day for decades, not just during this pandemic.

Wearing N95s are not a serious problem. For decades hardware stores have sold them for use by painters and woodworkers who wear them for at least that long on active jobs.. They also sell masks rated S95 that even protect against many fumes. If a particular N95 is uncomfortable, try a different brand, size or shape. A mask that fits properly will not restrict your breathing much at all.

I imagine I could get by in a reasonably seditary environment all day. During my personal work I could not. Temperature alone makes a basic mask a struggle. I use much larger respirators with the vents for exhale so that I can wear it for any length of time.

 Masks with vents do nothing to stop the wearer from spreading what they have. They do release the hot carbon dioxide exhale better so your next breath is fresh. Responsibly, I can't wear a vented mask for covid. 

Science says cloth masks are up to 40% effective while real masks are 90%. To me 40% might as well be none at all. I absolutely recomend a n95. Wearing the wrong mask is just virtue signaling. 

Not uncommon in some industrial situations, although the variable conditions and physical demands mean it's not possible to say in all circumstances. Probable that there would be breaks taken in between. I have worn breathing apparatus in the chemical industry.

Yes. I've done so every day since mask mandates were put into place in my area. But I don't wear an N95. Masks are breathable, even one type of N95 masks have vents in them that let you breath. 

Front line workers wear them all the time, so you should be able to wear one with out having too many issues. I wore one for 8 hrs at my workplace (which is a physically demanding job) when the blue masks were unavailable.