Incorrect time format

[KoSik]

Hello,
I have a problem with the time format.

Function excerpt:

format = '%H:%M:%S.%f'
aktual=datetime.datetime.now().time()
 
try:
        timeON = datetime.datetime.strptime(str(aktual), format) - datetime.datetime.strptime(lampaTV.AutoON, format)
except ValueError as e:
        print('Time error1:', e)

This function is called about 4 times per second and works well but after 2-4 days it throws an error e.g.

ValueError("time data '20:42:11' does not match format '%H:%M:%S.%f'",))

I can't deal with it for a long time