I still have at least one Ruby-Throated Hummingbird visiting my feeders and I could get more for a couple of weeks according to my records from years past.
The experts recommend that we up the sugar content from 1/4 cup to 1 cup of water to 1/3 cup sugar to every 1 cup of water. The higher content helps them fatten up for the rest of their journey to the wintering grounds. This is especially helpful if the weather hasn't been great and there is a shortage of flowers blooming. Such as in my case due to the drought in my area.
If you live in the South I encourage you to maintain a feeder throughout the Winter. I know of one man who lives on the coast of South Carolina that had a Ruby-Throated Hummingbird spent the entire Winter visiting his feeder. I have a nearby friend who had two Western species show-up at her feeder. A Black Chin stayed from November to January and an Allen show-up in January. A couple from Alabama who band Hummers traveled to her home and caught the Allen. It had been banded in Chattanooga, TN a couple of weeks earlier.
Even if you don't live in the South it is advised that you leave the feeder up for at least 2 weeks after seeing your last Hummingbird. You never know you may help out one that had fallen behind.
Note about my photo: I took this a couple of days ago. I don't know why this female sports a dark spot on her breast. Maybe she was attacked by a Praying Mantis???
Peace, Health, Wealth, and Love to ALL!