Date & Time Filter in Query entity for tasks

You will need to create two filters in your logical expressions. 

1. Where the requestedOn time is greater than the start of the day. i.e. 00:00:00 hrs
2. Where the requestedOn time is lesser than the end of the day. i.e. 23:59:59 hrs

This could be an alternative:

a!queryFilter(
        field: "requestedOn",
        operator: "between",
        value: {
          userdatetime(year(now()),month(now()),day(now()),0),
          userdatetime(year(now()),month(now()),day(now()),24)
        }
      )