To be honest, if I had a job that cut out even half-an-hour of my own spare time, for four days a week, I would have to urgently reconsider my "work-life balance". If you want a laugh, try the e-book "A year of living Danishly" which goes into this extensively. If it is a long commute, you could try finishing short of your destination or starting part-way along and running a piece.
I looked this up in the fairly famous ultra book (in a small world) "Relentless Forward Progress" by Bryon Powell, who is well known because of the website irunfar.com and his many video interviews on ultras. He claims a 100-mile program is appropriate. He gives two: one based around about 50-mile/week level, another for 70, although peak mileage may be a bit higher in spots. In general, the plans are more "lumpy" than shorter ultra plans, with a bit more emphasis on B2Bs, longer long runs, tune-up ultras like a 50k and 50 mile, less speed work and a general shift of mileage towards the weekends.
You can get the book as print or an e-book, or there are other 100-mile programmes on the net. If by running as a pair you mean you are sharing the 24-h between you then you could choose a shorter plan from the same or another source.
After a long run in snow at around +2C i have completed 219 km.
Last time I wrote about Marcus Aurelius. Well, now in 219 AD an emperor called Elagabalus was made Roman consul. He was assassinated at age 18. In between, he was apparently very eccentric, decadent and zealous. So much so that a historian wrote, to quote wikipedia: ""The name Elagabalus is branded in history above all others" because of his "unspeakably disgusting life.""
Sounds like Elagabalus had the ideal qualities for a trail runner. I can't find out what was so bad because "Elagabalus' vices were "too disgusting even to allude to them." Maybe he didn't wash his kit after every run.
Some GPS watches will auto-lap by location but not apps AFAIK. If you really really want an app I suggest you get one where the auto-lap can be set to a user-defined length (i.e., 400 m) and hope that it comes out correct. If you're basically just using it like a knitting counter it will be close enough to know when you are approaching the finish line.
If you press a manual stop as you cross the finish line you will know the time exactly. If you can accept GPS error for the purposes of training then just define a 5 km session in the app. I know some apps speak the auto-lap as that is one of the joys of road-racing in a crowd. It could be runkeeper or runmeter but someone will be along to correct me.