How do I convert a particular time to a UTC time in python?

Question

Currently working on a project where I need to manipulate a particular store's opening and closing times to UTC in Python. The opening and closing times are date independent.

For instance , I have a opening/closing times as

00:00:00
00:10:00

I'd like to convert this time to UTC

20:00:00 UTC
20:10:00 UTC

and compare the result with the store times noted in a database to identify if a store was open in the open/close times it should have been open in.

I've used the following code to convert these

    local_tmz = pytz.timezone(y["timezone_str"])
    time_str_start = x["start_time_local"]
    
    time_format = "%H:%M:%S"
    naive_start_time = datetime.strptime(time_str_start,time_format)
    local_start_time = local_tmz.localize(naive_start_time,is_dst=None)
    utc_start_time=local_start_time.astimezone(pytz.utc)
    print(utc_start_time.strftime(time_format),x["start_time_local"] ,y["timezone_str"])

y = Object containing timezone info of a particular store_id(In this case America/New_York)

x = Object containing opening/closing times of the particular store.

The output however is like so

4:56:00

The time conversion is off by an hour.