Well, it doesn't hurt to do a second one because they can technically ask for analysis of two related texts. Like you said, they most likely won't, but they do want you to study two so it's entirely possible. If you're looking to save time, use a poem instead of a novel. My second related text was The Waste Land by T.S Eliot, which was great because whilst it's a long poem, I was studying Eliot's poetry in Advanced so I knew about the central themes and concerns in his writing. This meant I could save time in a big way by only having to analyse Eliot from a Worlds Of Upheaval lens rather than a Critical Study of Literature one.