once title is issued.
Approvals generally only last 3 months, but most contracts require settlement within 14 days of the sub-division being registered - which is way too short so make it at least 4 weeks.
Just make sure that you keep tabs on how the building is going so you can start to organise valuations/finance before the titles and occupancy certificates are issued.
No extra fee's but when the property is nearing completion, have your banker/broker start the finance process to allow time for the standard finance conditions to be approved. Once occupancy is granted the loan can be finalised.