How long "should" a 19 min. (1.75 GB) 1080p project take to export?

I have a MacBook Pro with the following specs.

2019 - 16" MBPro
Processor: Intel i9 2.3 ghz 8-core
Memory: 32 GB RAM
Graphics: 
AMD Radeon Pro 5500M 8 GB
Intel UHD Graphics 630 1536 MB
Storage: 1 TB SSD (>300 GB free space) 

Running all latest versions of everything. 

I was recently hired to do a daily edit (5 days per week) for a YouTube "content creator" whose channel suddenly went from a few thousand subs to >200K. 

His daily show is a ~20 min. news broadcast.  When I first got the gig, I knew straight away that his visual aesthetic was on the weak side of amateur. So, I knew that I could eventually work with him to upscale his visual presentation several notches. 

I think I maybe made the mistake of a lifetime. Because... prior to the changes I suggested... his daily episodes took 5-7 min. to Export from FCP. I made two changes... and now each episode takes almost 2 hours to export. I am very computer savvy, with a background in programming and web development. But... as far as I can tell... Final Cut pro does not make it possible for me to view any kind of logs or performance charts during or after an export. The only thing I can see to do is just... export the project, and watch the little Background tasks go from 0% to 100%. If one export takes 2 min. and then another export takes 2 hours... there is not a way that I can see to find out what made this difference. 

Basically the episodes are all the same. 

1. Dude reads a lot of websites and online newspapers.
2. Dude combs through reddit, telegram, and some quasi "deep web" stuff. 
3. Dude collects a lot of screenshots, short video clips, and photos. 
4. Dude makes video... taking to camera.
5. During this video he just leaves the camera running... and he makes all his mistakes and says a million "uhms" and "mmmm's"... and he calls out to me (*the editor) when he wants me to insert which of the aforementioned "assets"... such as... "Insert Photo 3, here." 

I receive a 1+ hour long .mov file + all the aforementioned clips, photos, etc. 
I use TimeBolt to help me quickly remove all silence gaps, restarts, and mistakes. 
I get it down to between 15 - 20 min. 
I insert the articles, photos, and screenshots... adding a "Ken Burns" effect to pretty much all of them. 
And I add some super easy Text Titles and some Like and Subscribe motion graphics etc. 

Then I could export it all in 5-7 min. 

Then... I got the idea to use the "Keyer" effect to remove the background. He films each episode against a blue wall in his apartment. So... I take all 50--60 clips in the end, and I combine them all into one mega compound clip. To this clip, I use Color Finale 2 to color correct his skin tone and raise the exposure, since he is always way too dark. Then I add the Keyer effect and do a little moving of the sliders to get it looking good. 

It actually works quite well. Then I use the Generators > Backgrounds > Drift... animated Motion Graphic background... and I drop in some lower thirds, etc... and suddenly... the 5-7 export time goes up to 1-2 hours!!! I use the activity monitor to make sure everything that can be closed is closed. I uninstalled Chrome and got rid of all the Keystone elements it installs. I had NO IDEA that the Keyer effect + a tiny bit of Color Finale Pro could do this to the export time. Since Apple does not give my ANY documentation or analytics to go on... can anyone of you guys help me possibly get this export time down?

I did go ahead and export a 20 min. .mp4 video of just the background so that I could drop that in... and not have the computer needing to render and process that each time. But that honestly did not seem to do much to help. MAYBE saved a few min. of render time. But... I'm not really sure. 

I tried exporting to the lower 720p resolution, even through the projects are all shot and edited in 1080p. 

Anyone have any other suggestions? it's killing me to have to finish these loing edit sessions and then wait 1-2 hours while they export. I'm going to bed after 2:00 am every night. HELP!!!  

Exponential degradation in render performance can happen if an effect is placed lower in the stack and that effect is "temporal", IOW it processes a sliding window of frames. Examples: Neat Video, Digital Anarchy Flicker Free, etc. This can cause all effects above it in the stack to be recursively recomputed, once for each frame in the sliding window -- for each frame in the timeline. The keyer or something in Color Finale 2 may be doing that.

The first step is to duplicate the timeline, open the duplicate and cut out a small piece of it which reproduces the problem without taking 2 hr. That enables more rapid turnaround in successive tests. Next, verify the (say) 2 min. timeline takes too long to export.

Then examine the order of effects in the stack for each clip in the small timeline. Move any likely multi-frame effects to the top of the stack.  There is no documentation for which effects do that; it's just deduction and observation. After moving those to the top of the stack, see if exporting the short timeline becomes faster.

A separate issue regards an interaction between some effects, the Motion runtime engine and render cache, which can inhibit use of render cache during export. Generally if the timeline is fully cached, then you export, FCP should use the cache instead of recomputing the entire timeline. However, in some cases it will unnecessarily recompute all effects on clips. That is apparently related to an interaction between the Motion runtime engine and cache system.

E.g., say you put only Neat Video on a clip. That takes a while to render to cache, but exporting the timeline does not recompute that, and export is fast. Then you add a basic title effect to that clip and modify the title text, then you render that to cache with CTRL+R or via background render. Despite the rendered state, when exported, it will recompute that clip. Multiply that by 50 clips, and it's the difference between minutes and hours.

There are other possible causes, but given your symptoms and problem history, these two areas are the ones I first suspect.

The inability for diagnostic tools to find what aspect is slow is a generic problem on MacOS. Windows has had sophisticated end-user performance monitoring tools since NT 3.1 was first released in 1993. There is nothing like that on MacOS, even today.

XCode Instruments works very well but is designed for developers with source code and fully-symbolicated builds, not for end  users.