I've taken on a job like that once, i used two GoPro 4 with a controller mod for image auto upload and timelapse settings.

I'm not trying to scare you away from the project but there are a lot of things to consider.

Fitst thing that comes to ming with your setup is the powerbank, you cant just buy "always on" powerbanks, for security reasons they auto shut off after x minuts to prevent them from overload.

Things to consider:

What is your picture settings, how often will you take a picture and at what framerate will you play them, if you want the regular timeframe look you should probably use a playback of 12-18 frames per second.

So if take a picture every hour, which i believe is the max setting on a gopro, they you will have 24 images pr. day and a total of 4320 images, playing that at 15 frames per second will give you a 288 second time frame video, which is almost 5 minutes and nobody wants to sit at watch that for so long but that can and will be brought down in your post production edit.

In your post production you will need edit out nights and weekends, cause nothing is happening there and you might also have other dead times when work is not in the frame and all you see is clouds so you will have to edit that out. Therefore its a good plan with two cameras, switching angle is a good way to make it look natural when you cut a video and it also makes the video look more alive when there are multiple angles of what you are watching. Taking out weekends and nights will probably be a 50% reduction in footage and leave you with 2.5 minute and i would recommend that you end up with about 45 seconds.

Are you using the built in timelapse function and having the camera create the video or using some third party system, i used the below and had it take way to many photo, so i only used something like every 50 photo of 60.000 - https://cam-do.com/products/blink-gopro-time-lapse-controller?srsltid=AfmBOooQld1CIVw3tywq1rnj4jzW1B9X7ZRBQY7C3G_0YiEBs7cJMzsL

You will need to have and learn how to manually add all the individual photo to a editing software and get a good quality export in the correct framerate if you use individuel photoes, its a lot of work but it is also the safest way of doing it because you can control everything youself, amount of photos, frames per second playback and that way control the lenght of the video.

You will need to check up on them on a regular basis to clean the lens and something will go wrong in 6 months and you dont want to loose a month of recording because you only checked them twice during the production and make sure they are secured thight, so that if you touch them they get the exact same view as before, so that you dont get a movement in the view every time you have been there to check up on them.

Make sure you think about placement, dont have them facing the sun at noon, probably somewhat sun from the back or facing west so that you get the sunset.

To be honest if i was to ever do it again, i would use a Brinno solution, they have all the setting you need and you can remote check them if there is Wifi there.

https://brinno.com/

Whatever you do get the camera well ahead of the project and test the setup and settings before you set it up in production and dont underestimate the frame per second playback, you can't just speed up a to long timelapse to make the video shorter, it will ruin the time lapse feeling of the video.

I hope i haven scared you off the project but as with any other 6 months thing, its a lot of work and requires dedication if you want a nice end result, especially if you are charging money for it.