Tegan's right, it depends how sever the tongue tie is.
Milo had a mild one, but his attachment was causing me so much pain that I had it properly assessed, and they snipped it, when he was 6 or 7 weeks old.

MIL said DH had one too, but he wasn't breastfed past 5 weeks, and it was never snipped - it didn't affect his speech at all.