Metaphors are common in both literature and day-to-day conversation, as they help us to grasp abstract concepts. The most common metaphors are sometimes called conceptual metaphors; they are so common that we often forget they are metaphorical at all. One major conceptual metaphors is to think of time as a physical, moving entity (e.g. time flies, time marches on). In Marvell's "To his Coy Mistress," he refers to time as occupying a winged chariot, which suggests that time moves very quickly. This phrase may also be understood as an allusion, specifically to the Greek sun god, Helios, who flies across the sky in a chariot.
In the case of "To His Coy Mistress," the speaker of Marvell's poem is using the concept of time's swiftness to attempt to convince his mistress to sleep with him. Although he believes that she is beautiful, he wants to remind her that beauty is fleeting, given the effects of time. He also reminds her that death is an inevitability and that they should make the most of their time on earth. Here, time is linked with the idea of aging and death, and by underscoring time's swiftness, he hopes to convince her to sleep with him soon.