How soon to expect birds?

It depends on what area you live and what seed you put out. It's difficult to give an exact answer without more specifics. However I wrote to remind you to put anti-predator devices on the feeder post. Here locally, the Girl Scouts use gallon empty milk jugs tied together with string and then wrapped around the post to prevent squirrels from jumping into the feeder. There is a certain height for that; sorry I don't have the number handy.