Home loan deposit.

Nicole
Just wondering - does anyone know when you need the exact amount of the 20% home loan deposit? 
I can't get in contact with the woman from the bank sorting out my home loan, so I thought this may be a good place to ask.
We are unsure of if we need the 20% before our land settles (our land and home loan are together) or if we will need the 20% just as the house is completed and we begin paying off the loan. 
If anyone knows the answer that would be fantastic, I've been trying to get in contact with her for days and haven't been able to.