Let's analyze each sentence to determine the correct tense.
1) Lisa wasn't reading a detective story yesterday at 11 p.m.
Translation: Лиза не читала детектив вчера в 11 вечера.
Explanation: The phrase "yesterday at 11 p.m." indicates a specific time in the past when the action was in progress. Therefore, the past continuous tense (was/were + verb-ing) is appropriate. Since the sentence is negative, we use "wasn't reading".
2) Lisa didn't read a detective story at the weekend.
Translation: Лиза не читала детектив на выходных.
Explanation: "At the weekend" indicates a completed action in the past. Therefore, the past simple tense is appropriate. Since the sentence is negative, we use "didn't read".