For what it's worth, I was reading about this is the New American Commentary and this is what it says:
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Amos 5:13 (New American Commentary)
Interpreting v. 13 presents several difficulties. The semantic range of the three key words the NIV translates "prudent," "keeps quiet," and "evil" allows for several interpretations. The word "therefore" (laken) usually introduces a judgment message in the prophets and elsewhere in Amos (3:11; 4:12; 5:11,16; 6:7; 7:17). Yet the word maskil ("prudent"), except when it designates a type of psalm (Ps 32:1, etc.), refers to a person with insight or understanding (cf. Prov 10:5,19; 14:35). Therefore many interpreters consider the verse a wisdom saying rather than an expression of judgment. Silence, however, is not recommended in the verse. Certainly Amos was not silent in his time, nor were those referred to in v. 10, though silence would have been the safest and easiest course. Although speaking out might be a waste of effort, the righteous could not keep silent. The point could be that the times were such that wise men, who in better times would be consulted for their wisdom, were silent because no one would listen. Or the term maskil could be a morally neutral reference to one who knew how to avoid trouble, in which case silence would be the best policy in such evil times.
The word translated "evil" (ra'a) likely means here "disaster, calamity," as in 3:6; Ps 37:19; Jer 15:11; and especially the end of Mic 2:3, which is identical to the last line here. "In such times" is literally "at that time," and "the times are evil" is "it is/will be a time of evil/disaster." The time referred to, then, is perhaps the future divine judgment when the prudent or thoughtful person will be stunned to silence by such disaster (cf. Lam 2:10; 3:28). The verb translated "keeps silent," yiddom, may even refer to the silence of death and be translated "will perish" (cf. 1 Sam 2:9; Ps 31:17; Jer 8:14; 25:37; 48:9; 49:26; 50:30; Zeph 1:11). Perhaps the prudent will perish "because the times will be so bad that goodness will not be tolerated."
G. Smith has argued cogently that since the root of hammaskil (sakal) can mean "to be clever" or "to prosper," the meaning of the noun here that best fits the context is "the prosperous." This would make the word refer to the very people Amos had been describing who used their position, power, and wealth to oppress the poor (v. 11). Smith translates the sentence: "Therefore, the prosperous will be silent at that time, for it will be a disastrous time." This silence he takes either as the silence of grief or of death. Whatever details of interpretation are adopted, it seems clear that the verse is a prediction of judgment."
