It depends... if it is a leasehold property where state govt approval is needed before the transfer, it will take longer.

If the owner is in the midst of refinancing when he sold the property it will also take a long time, as the house has to be discharged from the old financier, charged to the new financier before it can be transferred to you..

best to ask the owner if he has charged the property and whether he's in the process of refinancing.