<p-calendar readonly="true" [showTime]="true" inputId="time" [hourFormat]="24" [minDate]="minDate" [maxDate]="tomorrow" inputId="range" [(ngModel)]="obj.date" formControlName="selectedDateTime">
Readonly property doesn't exist in p-calendar. You can use the "disabled" property instead.
<p-calendar
disabled="true"
[showTime]="true"
inputId="time"
[hourFormat]="24"
[minDate]="minDate"
[maxDate]="tomorrow"
inputId="range"
[(ngModel)]="obj.date"
formControlName="selectedDateTime"></p-calendar>