Considering 0.5mgs of finasteride gives 80% of the effect of 1mg and the halflife is relatively short, wouldn’t better results be achieved from taking 0.5mgs once every twelve hours?
I doubt that 0.5mg taken twice a day would be much different than a once a day 1mg dose. I suppose it could be tried, but wouldn’t having to stick to taking half a pill every 12 hours be a little annoying?