If we will find them then this is an intersection on our technology advancements and proximity of such lifeforms, considering how little effort is currently put on space exploration it will take extremely long, things will probably accelerate when we find alternatives to the primitive combustion engine that makes fuel tanks bigger than rockets and makes the process very expensive.

If they will find us and this only means more advanced intelligent life then this obviously can happen any time or might already happened and can be delayed by us not being considered ready/worthy for contact or according to many conspiracy theories our governments considers we are not ready.