About 60 minutes

I spent around 7 years at 30 mins/day - I was happy with it there, it was more of a casual thing for me at that time. Then I read some books, starting with The Mind Illuminated, and increased to 1hr/day over 4-5 months.

I find the act of effort or willpower for me is starting to meditate in the first place. Once I'm meditating, 60 mins doesn't require any more discipline than 30 mins, in fact it feels better.