Thinking that plants are out there, figuring out the time of day, or the seasons in the year can be a lot to wrap your head around. Plants are actually pretty dynamic, and they move around a lot! They have complex mechanisms for not only detecting light, but also following light as they grow.
The main advantage of using light perception for flowering time in plants is for reproduction, so that birds and bees can pollinate flowers during the spring. Other animals use the amount of light during the day, or photoperiods, for knowing the optimal time of year for reproduction, and to prepare themselves for the harsh winter up ahead. Different plants (and different animals!) will have unique photoperiods to which they will respond