OET interlinear HERO (JDG) 20:15

uW Translation Notes:

Note 1 topic: figures-of-speech / metonymy

בַּ⁠יּ֤וֹם הַ⁠הוּא֙

(Some words not found in UHB: and,they_were_mustered sons_of Binyāmīn in_the=day (the)=that from,the,cities twenty and,six thousand (a)_man draw sword apart,aside from,the_inhabitants_of of_(the),Gibeah rallied seven hundreds (a)_man chosen )

This probably took more than a single day. The author seems to be using the term day by association to mean a particular time. If it would be helpful in your language, you could use an equivalent expression or plain language. Alternate translation: [at that time]

Note 2 topic: figures-of-speech / explicit

אִ֥ישׁ בָּחֽוּר

(a)_man (Some words not found in UHB: and,they_were_mustered sons_of Binyāmīn in_the=day (the)=that from,the,cities twenty and,six thousand (a)_man draw sword apart,aside from,the_inhabitants_of of_(the),Gibeah rallied seven hundreds (a)_man chosen )

The author assumes that readers will know that these men were specially selected because they were the best soldiers. You could indicate this explicitly in your translation if that would be helpful to your readers. Alternate translation: [elite troops]