12 hours to 24 hours conversion function

I have made a time format converter which converts 12 hour format to 24 hour format. My convert_to_24() takes a string in format of HH:MM:SS followed by AM or PM. It returns a converted string to 24 hours format without the AM/PM string.

Note: Let us assume that input will always have no space between them e.g. 07:05:45PM, not 07:05:45 PM

def convert_to_24(time):
    """str -> str
    converts 12 hours time format to 24 hours
    """
    return time[:-2] if time[-2:] == "AM" else str(int(time[:2]) + 12) + time[2:8]

Sample usage:

>>> convert_to_24("07:05:45PM")
'19:05:45'
>>> convert_to_24("10:47:00PM")
'22:47:00'
>>> convert_to_24("02:35:36AM")
'02:35:36'
>>>

Can my function be made even better? By better I mean better in way of performance, design etc.

This function is not just cryptic — it's also wrong. I would expect convert_to_24('12:00:00AM') (midnight) to be '00:00:00', but it returns '12:00:00' (noon).

StackExchange Code Review Q#111596, answer score: 11