I guess there are other variations for this expression that one can google out on the Internet such as "Make today your someday" and "Make that someday today". However, is it possible to find out its origin?
I can't say anything for a definitive origin, but I typically hear this as a direct response to a phrase such as "that will happen some day", an admonition indicating that the speaker is trying to avoid pinning down a day due to laziness. I don't think that there is a specific origin so much as that it's a rephrasing of the initial statement. Consider the following:
"I'll finish the project some day" "Well, make someday today. We're in a hurry."