Full sun exposure will not allow them to start since when it falls from the tree it’ll be rooting under all the shade of the overgrown. However they can handle increasingly more sunlight afterwords.

For time scale for me is 2 months for leaf to sprout and seed sprout as well if fresh seeds.

They are indeed very slow to grow with a years time my plants are maybe 6-8 inches tall. I however do not leave them in high humidity but rather normal humidity of around 60-80% and they are in the same light conditions of my cacti. They will grow better in higher humidity and shade however I prefer to provide my plants the conditions they will live in long term.

The main thing they need is water. Despite how slow they grow they love constantly moist soil. They will quickly let you know by drooping and looking sad and a quick watering will perk them back up. I water every 3 days or so unless was very cloudy then once a week.

Fertilizing also helps them grow nicely but keeping low amounts to prevent burning. I forget to feed mine more often.

My soil mix is 50/50 top soil and gravel with some moss on top few cm so the roots had an easier time