compare/check date that it lies between two dates or not || Use of .getTime() object of Date

function saveRecord(context) {
    var rec = context.currentRecord;
try{
    var startDate = rec.getValue({
      fieldId: "custbody_clb_periodstartingdate",
    });
    log.debug("startDate=",startDate);
    var endDate = rec.getValue({
      fieldId: "custbody_clb_periodendingdate",
    });
    log.audit("startDate", startDate + "endDate" + endDate);
    /*  startDate = new Date(('0' + (startDate.getMonth() + 1)).slice(-2) + '/'
                    + ('0' + startDate.getDate()).slice(-2) + '/'
                    + startDate.getFullYear());
         endDate = new Date(('0' + (endDate.getMonth() + 1)).slice(-2) + '/'
                    + ('0' + endDate.getDate()).slice(-2) + '/'
                    + endDate.getFullYear());*/
    /* startDate = format.parse({
            value: startDate,
            type: format.Type.DATE
        });
         endDate = format.parse({
            value: endDate,
            type: format.Type.DATE
        });*/

if(NullCheck(startDate)&&NullCheck(endDate)){        
    var lineCount = rec.getLineCount({
      sublistId: "time",
    });
    log.audit(
      "line Count",
      lineCount +
        "startDate" +
        startDate.getTime() +
        "endDate" +
        endDate.getTime()
    );
    for (var t = 0; t < lineCount; t++) {
      var apply = rec.getSublistValue({
        sublistId: "time",
        fieldId: "apply",
        line: t,
      });
      // log.audit("apply",apply)
      if (apply == true) {
        var date = rec.getSublistValue({
          sublistId: "time",
          fieldId: "billeddate",
          line: t,
        });
        /*date = format.parse({
                    value: date,
                    type: format.Type.DATE
                });*/
        log.audit("fdate", new Date(date) + "date less tha" + date.getTime());
        log.audit(
          "Less Than",
          Number(date.getTime()) <= Number(endDate.getTime())
        );
        log.audit(
          "Greater Than",
          Number(date.getTime()) >= Number(startDate.getTime())
        );
        // if((date <= endDate) && (date >= startDate)){1673424000000  1674115200000  1673942400000
        if (
          Number(date.getTime()) >= Number(startDate.getTime()) &&
          Number(date.getTime()) <= Number(endDate.getTime())
        ) {
          log.audit("Into");
        } else {
          alert("Selected Billable Time's Date is Out off Service Period.Please apply only within period Billable Times");
          return false;
          // var myCustomError = error1.create({
          //   name: "OUT_OFF_DATES",
          //   message: "Selected Dates Are Out off Service Period.",
          //   notifyOff: true,
          // });
          // log.error("Error: " + myCustomError.name, myCustomError.message);
          // throw myCustomError;
        }
      }
    }
  }
}
catch (e){
  log.error("error in saveRecord",e)
}
    return true;
  }