Meditation is so diverse in reality you have to find your own path. I have been meditating for many years and have attended training camps on meditation and in a nutshell this group told us the optimum time is very early morning and outside if possible. They start at 4 pm, before light, but I think anytime early morn is fine. I have tried 4, 5 and 6am, as long as it's dark and quiet it is fine for me.
I have sat more times then I can remember at 4am in the rain outside.....those were some of the best times though actually. The amount of time is a preference, it depends how long it takes you to get to the place you are trying toget to. I have played around with times from 10 mins to 2 hrs, and I use 22 mins at this point....
Good luck, like I said it is your own path, mine is early outside if possible, very quiet and 22 min.......Peace