Fastest way to remove the first x characters from a very long string

[bruceg113355 at gmail.com]

I have a string that contains 10 million characters.

The string is formatted as:

"0000001 : some hexadecimal text ... \n
0000002 : some hexadecimal text ... \n
0000003 : some hexadecimal text ... \n
...
0100000 : some hexadecimal text ... \n
0100001 : some hexadecimal text ... \n"

and I need the string to look like:

"some hexadecimal text ... \n
some hexadecimal text ... \n
some hexadecimal text ... \n
...
some hexadecimal text ... \n
some hexadecimal text ... \n"

I can split the string at the ":" then iterate through the list removing the first 8 characters then convert back to a string. This method works, but it takes too long to execute.

Any tricks to remove the first n characters of each line in a string faster?

Thanks,
Bruce