I have lived in Texas for 38 years, about half of that time in South Texas and half in Dallas. It's been only during the past several years that I have been hearing/reading "on" attached to "yesterday", "today", "tomorrow", "last month", "next week", etc. It seems to be only African-American individuals, regardless of educational level, who present this usage. I am annoyed by what I consider poor use of the English language and wonder why some people resort to it.