The first log you need is the first one which started after the data-copying portion of the full backup completes. That's usually very close to the end of the backup. The only time you usually need to worry is when the full and a log backup complete around about the same time

That said, there's no harm in being safe and starting with one log earlier. If it's not required SQL will give you an error message saying that the log file is too old. It won't mess up the restore sequence or cause other problems.