Welcome to the forum patrip.
you can time how long you can record with a camera by the files on the full memory card, by looking at time/date stamps of the video files ( most easy if you do one long session, maybe at home powering the system with a wall USB charger )
You can then set a countdown alarm on your phone to pull over and DL footage to a laptop, or swap memory card.
The suggested A139 do not have a screen, so you need to connect to it with wifi to set it up ( mostly setting your time zone +/- daylight savings - selecting image quality / bitrate which should always be the best one - select file size, most popular are 3 minutes i think )
But generally the LCD screens can turn of automatic in seconds,,,, and so they should.
The A139 however are not that portable as it rely on the 3 cameras to be glued in place, actually there are very few cameras nowadays that use a suction cup.
So you should maybe look at one of the 2 in 1 systems where the cabin camera are part of the front camera / main unit, the downside to these are you often have to mount it in a less decidable location ( low on the windscreen ) so the cabin camera are not just filming the "back" side of your mirror.
In general the best place for dashcams are top / middle of windscreen, though that are not often possible due to sensors on the windscreen, in that case you have to offset a little to one side.
I recommend you loosely power up the camera so you can see on screen or live preview on phone where the most optimal place are so you dont have too many things in view,,,,, the wide angle lenses do meaan that you cant just offset to right next to a sensor housing, you have to be a little off it or it will be in the footage.
You can always use a suction cup adapter for glue on systems, and then glue to that instead of the windscreen and so have a removable system.
Many little files are no problem, you can import a drive made up of 273 three minute files into any video editor, then drag all those tiles to the timeline and when dropped there they should be in cronilogical order by the file names. Then you can output them all as one seamless long video if you desire so, i recommend to split up onto 10 - 15 minute long segments.
you probably want to speed up some segments of the drive anyway, as no one want to sit thru your XX hour long drive at 1:1 speed.
I like to speed up so 1 hour of actual time last 10 minutes or so, this is still fine for winding open big roads, you can then edit interesting parts to be at normal speed.
Example of speed up drive video, here with additional information overlaid.