Most bonsai work is seasonal. 'When' can man what time of year. You obviously know what season it is now where you are but we don't. Could be giving you reverse info for pines. Add a location to your personal profile so other members can give you info that suits your area.
'When' can also mean at what age to do things to your pine. We really need to see where it is up to to be able to give meaningful and useful advice.
As
@Treefer says, pictures will help a lot.