What does 2 Samuel 4:5 mean?

Rechab and Baanah, the sons of Rimmon from Beeroth, went to Ish-bosheth's house during the hottest part of the day, when he was taking his midday rest. 2 Samuel 4:5 - Modern Text Bible

(The two brothers decide to act while Ish-bosheth, Saul's son and the current king, is vulnerable—sleeping in the afternoon heat.)