Nectar in hummingbird feeders should be replaced every 3 to 5 days, especially during hot weather, as the sugar solution can spoil quickly. If the feeder is in a shady location, it may last a bit longer, but it's important to check for cloudiness or mold regularly. Additionally, clean the feeder thoroughly with hot water when you replace the nectar to prevent the growth of harmful bacteria.
Not often if there tarting to wear and tear you should replace them.
to eat
Nectar
Because they don't need animals to polinate. If they make nectar or have bright colours and strong scents, it will be an animal-polinated flower. So they don't need to make nectar or have bright colour
There is no definite time that you need to replace a convertible top. If it is properly maintained then it can last for many years.
They need replaced when they wear out.
when its empty
In order to extract nectar from a flower you will need to use a small tube device that has a suction feature. You will suction the nectar out using the tube.
When your tires have 2/32" tread depth left you need to replace them.
No set time...just at failure
Nectar is produced by flowers to attract insects, bats or birds that will help to carry its pollen to other plants (and bring fresh pollen to it). If a plant is pollinated in the wind, then it doesn't need to spend the energy to make nectar.
Bees collect nectar for food. Because raw nectar would not store for very long without fermenting, bee convert the surplus of nectar they collect into honey to use as food when nectar is not available. It is this surplus honey that we collect. Beekeepers then replace the honey with sugar syrup which, for the bees, is just as good.