In Sonnet 18 and Sonnet 116, Shakespeare conveys ideas about the effects of time in different ways.
In Sonnet 18, Shakespeare uses vivid imagery and metaphors to suggest that time can be destructive, but that the beauty of the beloved can transcend the ravages of time. The speaker describes the summer as a time of change and instability, subject to the "rough winds" of fate, but he contrasts this with the beloved's eternal beauty, which is like the "eternal summer" of the poem's final couplet. The poem suggests that time can wither and destroy even the most beautiful things, but that love and art can preserve them for eternity.
In contrast, Sonnet 116 takes a more optimistic view of time, suggesting that true love can withstand the passage of time and remain constant even as everything else changes. The poem argues that love is not subject to the "edge of doom" and is not affected by "Time's fool," but rather endures even in the face of adversity. The speaker suggests that love is an unchanging force that can transcend the effects of time, and that it is the most powerful and enduring force in the universe.
Overall, both Sonnet 18 and Sonnet 116 convey the idea that time can have powerful effects on the world and on human beings, but that love and beauty can transcend these effects and endure even in the face of adversity.