RBG's reply is correct as far as a 'classic', training or 'textbook' approach goes for many airlines. As he has indicated, in the real world, one rarely gets to fly such an approach.
'Gear down' can be required at many stages of an approach. The earliest I have expoerienced is 80 miles from landing due to a need to reduce landing weight. Putting it down at 10000 ft or so is not unknown, particularly when a sudden change in landing runway (probably due to the national carrier wanting a 'straight-in approach' on the runway 'not-in-use' and a change to a sudden 'calm' wind from the original 10 knots down the runway
) leaves one incredibly high on the approach profile and needing extra drag. Personally I try to announce the forthcoming event to the salary payers if time permits so as to avoid any undue anxiety.
Most airlines specify a 'minimum' height for gear extension, commonly 1500' if visual with the runway or 2000' if not. Other than that, it is down to necessity/preference.