It is important to note that, in fact, the meaning of the diminutive form of words is more often metaphorical than it is literal. While both are valid, native Spanish speakers often use the diminutive, “-ito/a,” to add a sense of petiteness, cuteness or imply similar meaning to this.
In addition to the literal and positive metaphorical meanings, the diminutive can also imply a negative metaphorical connotation, such as in English. For example, in Cee-Lo Green’s song “Forget You,” he says “Why don’t you go run and tell your little boyfriend . . . ” In this case, the boyfriend is obviously not physically small, but Cee-Lo diminishes said boyfriend’s value in a negative way. This exact same usage can also be employed in Spanish to reprimand an unfaithful significant other, e.g. “ve y díselo a tu noviecito.”
Now, to your question regarding “ahorita.” This fits into a fourth category which at once encompasses elements of, but distinguishes itself from each of the aforementioned three: idioms. “Ahorita” is a colloquial idiom used mainly in American Spanish dialects, as opposed to Spain’s Spanish. “Ahorita” means “right now.” In Spain, it would be more common to say “ahora mismo”. Naturally, like in English, all variations are possible and could be said by a native depending on the speaker’s intention. I’ve even heard a native speaker say “ahora mismito” to add a sense of irony, but continue urging that something occur “right now”.
To reiterate, “ahorita” means “right now,” and has equivalent meaning to “right this second” or similar English phrases.
One final note is that while using this word is perfectly fine and quite common in informal contexts, it is probably best left unused in formal contexts, such as business letters and essays, where “ahora mismo” is largely preferred.