AusBonsai

When is the best time to airlayer a crab apple and a fig

I usually start air layers on deciduous just after the leaves are full open - October, November, maybe September?
You can make air layers at any time of year but not much will happen over the dormant time so it takes much longer if you start in autumn or winter.

Layer figs when they are active in late spring or summer. If it is healthy and you look after it it should only take a few weeks to get roots on a fig.

How long do you normally suggest leaving the air layer on deciduous shibui? Or is it just until the bag swells with roots? I have a big maple in my front yard (approx 3.5m high) I plan to do my first air layer on this year.

How long do you normally suggest leaving the air layer on deciduous shibui? Or is it just until the bag swells with roots

Every species will be different. Different areas and climates will be different. Even individual plants of the same species will be different because of differences in vigour, health, light levels, nutrients, etc so there is no magic length of time. Leave all layers until you are happy with the amount of roots in the bag. If you use transparent plastic you can see roots growing inside the bag. If you use opaque plastic and cannot see through you can gently open the bag every few weeks to check what is happening.
The beauty of layers is if you are not sure you can leave it a few more weeks until there are more roots.

Plants can survive with much fewer roots than we imagine. I have potted layers and cuttings with just a few small roots and they have kept growing.