Of course this is available, just in your timer trigger function do a get/post request. The below is my test code.

import datetime
import logging
import requests

import azure.functions as func

def main(mytimer: func.TimerRequest) -> None:
    utc_timestamp = datetime.datetime.utcnow().replace(
        tzinfo=datetime.timezone.utc).isoformat()

    if mytimer.past_due:
        logging.info('The timer is past due!')

    logging.info('Python timer trigger function ran at %s', utc_timestamp)
    url = 'your function url'
    PARAMS = {"name": "test"}

    response_decoded_json = requests.post(url=url, params =PARAMS)
    print(response_decoded_json.text)

I got the respond from the http trigger function, as for your requirement, change the cron expression to 0 0 21 * * *.

Update: I test this is available.

Timer Function code:

import datetime
import logging
import requests

import azure.functions as func


def main(mytimer: func.TimerRequest) -> None:
    utc_timestamp = datetime.datetime.utcnow().replace(
        tzinfo=datetime.timezone.utc).isoformat()

    if mytimer.past_due:
        logging.info('The timer is past due!')

    logging.info('Python timer trigger function ran at %s', utc_timestamp)
    url = 'https://functionname.azurewebsites.net/api/httptest?code=master key'
    PARAMS = {"name": "test"}

    response_decoded_json = requests.post(url=url, params =PARAMS)
    logging.info(response_decoded_json.text)

HTTP function code:

import logging

import azure.functions as func


def main(req: func.HttpRequest) -> func.HttpResponse:
    logging.info('Python HTTP trigger function processed a request.')

    name = req.params.get('name')
    if not name:
        try:
            req_body = req.get_json()
        except ValueError:
            pass
        else:
            name = req_body.get('name')

    if name:
        return func.HttpResponse(f"Hello {name}!")
    else:
        return func.HttpResponse(
             "Please pass a name on the query string or in the request body",
             status_code=400
        )

When upload the function remember add requests==2.22.0 in requirements.txt.

Suppose the main problem is about how to get the httptrigger function url. The url the main parameter you need is the Function APP name, function name and the master key(or default key). The Function APP name and function name actually you already know.

About the code(key), you could deploy any function firstly then, go to the manage page you will be able to get the code and paste after the url you will get the full http trigger url. Then upload the two functions, it will be okay.