I love when people who have low-grade hair loss come here and give advice. Consider yourself VERY lucky, just like the people who maintain for 15 years on Finasteride.
Do you think people would be using nuke-tier drugs if they could maintain with something as simple as RU or Propecia? We're buying and researching these untested drugs because we're masochists or something? There is no point being a concern troll and writing all these warnings while being a humble brag about how you maintained your hair for 10 years and still f*****g chicks left and right.
As far as the actual subject at hand..
It doesn't matter what RU's half-life is. What matters is that it is a piss-poor anti-androgen that is no longer developed for any purpose due to its low affinity that is outcompeted by DHT something like hundreds of times for its ability to bind to the AR. Once it is outcompeted on the first place you apply it (your scalp) it will then travel around the body and bind to whatever else it finds within those two hours of its precious half-life. Use RU consecutively for a few days at doses larger than 75 mg and then tell me about how you still even have a libido.
On the other side, a single dosage of Enzalutamide which has a half-life of 6 freaking days didn't impact my libido or cause gyno one bit, despite having an IC50 that is something like 60-70x (or more) lower than that of RU, and is only outcompeted by DHT about 2-3x.
How is that possible? Because due to the high affinity most of it bound to the first AR closest to the source of the application - which would be your scalp, exactly where you want it to. It's unfortunate that it also binds to GABA receptors, but that's where Darolutamide comes in! These drugs show that it is entirely possible to use very high affinity AR blockers topically and have success with a low profile of systemic (anti-androgenic) side effects, and that this is possible regardless of the half-life. Yes, it would be better if Darolutamide had a half-life of 30 minutes and not 10-15 hours, but a perfect drug is very hard to make.
In order for a drug to work as a hair loss topical the affinity is far more important than the half-life, because for a high affinity drug it is far more likely that it will bind close to where it is actually applied, which is what you want. You don't want it just falling through your scalp, not binding to anything due to being weak and then ending up in your bloodstream. Otherwise you may as well just take these drugs orally.