use python to convert MM:SS time format to .ass format

Something like this seems to do the trick:

text = """
02:42 02:47   And so that Wayne Gretzky method for sort of going into the future and
02:47   02:51   imagining what that future might look like, again, is a good idea for research.
"""


def convert_time(t):
    return f"00:{t},000"


for line in text.splitlines():
    try:
        start, end, text = line.split(None, 2)
    except ValueError:  # if the line is out of spec, just print it
        print(line)
        continue
    start = convert_time(start)
    end = convert_time(end)
    print(start, end, text, sep="\t")

The output is

00:02:42,000    00:02:47,000    And so that Wayne Gretzky method for sort of going into the future and
00:02:47,000    00:02:51,000    imagining what that future might look like, again, is a good idea for research.

Use regex sub for search and replace, \\1 corresponds to the part in brackets.

import re
text = """02:42 02:47   And so that Wayne Gretzky method for sort of going into the future and
02:47   02:51   imagining what that future might look like, again, is a good idea for research."""
print(re.sub('(\d\d:\d\d)', '00:\\1,000', text))

You might further specify the regex, e.g. with

print(re.sub('^(\d\d:\d\d)\t(\d\d:\d\d)', '00:\\1,000   00:\\2,000', text))

to avoid wrong substitutions. Check regex101.com to find the matching one for your data.