Set min and max time for ion-datetime

<ion-item>
  <ion-label position="floating">from</ion-label>
  <ion-datetime displayFormat="hh:mm a" pickerFormat="hh:mm a"
  [(ngModel)]="fromDate"></ion-datetime>
</ion-item>

<ion-item>
  <ion-label position="floating">to</ion-label>
  <ion-datetime displayFormat="hh:mm a" pickerFormat="hh:mm a" min="{{fromDate}}">
  </ion-datetime>
</ion-item>

above is my code, i am choose time for first one and set the selected time is minimum for the second one, i need this output but when i select pm i second datetime cannot work properly. what will do,please help to solve this.