With a mortgage broker this is also the case when your Loan officer actually submits loan to the bank it will take 24-72 hrs. depending upon bank. But this is only for a conditional approval.
Meaning they will give you a list of conditions to fulfill in order for approval to be finalized. You have 2 types in some cases 3 types of conditions. Prior to Doc conditions, Prior to funding conditions, and Prior to close or wire conditions in some cases. Your mortgage broker will work through these conditions, and you will get docs first. Then when docs are signed the lender gets them back, and asks all funding conditions are met. Then funding will take place, and then if they ask for last minute closing conditions you will fulfill those. Then property records next business day, and house should be yours.
If you have all of the needed info for a lender ( w2,pay stubs etc.) they can give you a pre approval in a short time period. If you are asking how long it takes to have the loan approved after application, that can vary. I work with a lender that can turn around a loan in 7 to 10 days, but it usually takes z minimum of 3 to 4 weeks.