I've noticed over the years you can tell who has been to your garden before and who hasn't.
The first few times they hover around the feeders and then take off, which allow you to release the breath you have been holding, as you silently chant "come on..come on" in your head.
It's like they are sizing up what you have to offer. Getting the feel for the area, that type of thing.
Once they have used the feeder a few times and are comfortable with your backyard, they will zip and zoom in at full speed then stop dead right over the feeder then zip right to the feeder port.
This is my experience anyways.
Through out the summer you will see they difference between the Hummers who know your feeders and the new ones coming in.
The same behaviour will be seen over the summer.
As for how full to fill the feeders.
That's up to you.
I have 3 feeders and usually only put about 1/4 cupin each. Which fills it about 1/4 full. I clean and refill at least once a week, twice a week when it is really hot and humid so I just think it's a waste to fill them up. They cannot drink it all anyways. So just put a bit in and keep it clean and fresh. Make up a big batch then keep it in the fridge. Every few days take out a bit, put it in a glass to warm up to room temperature then fill them. I take it out before I go to work then by the time I get home, it's the perfect temp to put outside in the feeders.
It saves a bunch of time.
Long response, I know, but hope it helped.
Meghan