getTimestamp.js

'use strict'

const moment = require('moment')
moment.locale('pt-BR')

let now   = moment()
let hour  = Number(now.format('HH'))

now.set({'hour': 21, 'minute': 0, 'second': 0, 'millisecond': 0})

if( !(hour >= 21 && hour <= 23) ){
    now.subtract(1, 'days')
}
let timestamp = now.valueOf()
console.log("timestamp: ", timestamp)