DY: As mentioned earlier, the Rema said that the German custom was to wait 1 hour, but he recommended doing 6 (I think the 1 hour might also be mentioned by the maharil, but I don’t actually know). The 3 hour custom really came out of nowhere.
Everyone agrees that if one is in the habit of waiting 6, he cannot switch to 3 even if it’s more in line with the customs of his ancestors, probably because the 3 hour has no source. I follow western Ashkenaz minhag, so I am, by no means, ‘out to get it’ or anything.