Je met de coté ici une petite classe technique qui permet de faire des opérations sur des horaires (addition, soustractions, division etc)

Elle était a la base faite pour un script google sheets du coup le jour où je veux l'utiliser il faudra se débarasser des classes de chez google (genre le Logger)

function test(){
  Logger.log("plus = 09:30 : ", new Time("08:00").plusTime(new Time("01:30"))) 
  Logger.log("plus = 10:00 : ",  new Time("08:00").plusTime(new Time("02:00"))) 
  Logger.log("plus = 08:01 : ",  new Time("08:00").plusTime(new Time("00:01")))

  Logger.log("minus = 07:59 : ", new Time("08:00").minusTime(new Time("00:01"))) 
  Logger.log("minus = 23:00 : ", new Time("01:00").minusTime(new Time("02:00")))  
  Logger.log("minus = 22:59 : ", new Time("01:00").minusTime(new Time("02:01")))
  Logger.log("minus = 22:58 : ", new Time("01:00").minusTime(new Time("26:02")))

  Logger.log("divide = 03:20 : ", new Time("10:00").divideTime(new Time("03:00")))  
  Logger.log("divide = 04:00 : ", new Time("08:00").divideTime(new Time("02:00")))  
  Logger.log("divide = 08:00 : ", new Time("08:00").divideTime(new Time("01:00")))

  Logger.log("modulo = 00:15 : ", new Time("01:00").moduloTime(new Time("00:45")))
  Logger.log("modulo = 01:00 : ", new Time("02:30").moduloTime(new Time("01:30")))

  Logger.log("asDate = AUJOURD'HUIT01:00:00 : ", new Time("01:00").asDate())

  Logger.log("asDecimal = 0.5 : ", new Time("00:30").asDecimal())
  Logger.log("asDecimal = 1.5 : ", new Time("01:30").asDecimal())
  Logger.log("asDecimal = 1.25 : ", new Time("01:15").asDecimal())

  Logger.log("fromDecimal = 12:30 : ", Time.fromDecimal(12.5))
  Logger.log("fromDecimal = 00:45 : ", Time.fromDecimal(0.75))
  Logger.log("fromDecimal = 01:45 : ", Time.fromDecimal(1.75))
  Logger.log("fromDecimal = 02:30 : ", Time.fromDecimal(2.5))  

  Logger.log("fromMinutes = 23:45 : ", Time.fromMinutes(-15)) 
  Logger.log("fromMinutes = 02:00 : ", Time.fromMinutes(120)) 
}

/**
* Représente une heure de la journée au format "HH:MM"
*/
class Time{

  /**
  * Constructeur.
  * Param : 
  *    hour:String - L'heure au format "HH:MM"
  */
  constructor(hour){
    this.hour = hour
  }

 /**
  * Initialise un Time à partir d'un nombre de minutes
  * Param : 
  *    mins:String - L'heure au format "HH:MM"
  */
  static fromMinutes(value){
    function addZeroToHour(hour, minutes){
      if(minutes < 0){
        hour -= 1
      }
      return hour >= 0 ? ((hour<10 ? '0' : '') + hour) : addZeroToHour(24 + hour)
    }

    function addZeroToMinutes(minutes){
      return minutes >= 0 ? ((minutes<10 ? '0' : '') + minutes) : addZeroToMinutes(60 + minutes)
    }

    var hour = (value/60 |0) % 24
    var minutes = value % 60
    return new Time(addZeroToHour(hour, minutes) + ':' + addZeroToMinutes(minutes))
  }

  static fromDecimal(value){
    let hour = Math.floor(value)
    let minutes = (value % 1) * 60
    return new Time((hour < 10 ? '0' : '') + Math.floor(hour) + ":" + (minutes<10 ? '0' : '') + Math.floor(minutes))
  }

  asDate(){
    var splitted = this.hour.split(':')
    let date = new Date()
    date.setHours(splitted[0], splitted[1], 0)

    return date
  }

  asMinutes(){
    var splitted = this.hour.split(':')
    return splitted[0]*60 + +splitted[1]
  }  

  asDecimal(){
    return this.asMinutes() * (1/60)
  }

  asHours(){
    return this.hour
  }

  plusTime(other) {
    return Time.fromMinutes(this.asMinutes() + other.asMinutes())
  }

  minusTime(other) {
    return Time.fromMinutes(this.asMinutes() - other.asMinutes())
  }

  divideTime(other){
     return Time.fromDecimal((this.asMinutes() / other.asMinutes()))
  }

  moduloTime(other){    
    return Time.fromMinutes(this.asMinutes() % other.asMinutes())
  }
}