In English, the pitch and rate at which one speaks typically do not affect the types of the tokens that one is using. Whether you say "home" quickly or slowly, with a low or a high pitch, your utterance is a token of one and the same type. But this need not be a universal truth. One can easily imagine a language where an utterance of "home" means one thing when spoken quickly and another when spoken slowly. In that case, there are two word types here, and which type one's token falls under will be partly determined by the sequence of phonemes and partly by the rate at which one speaks. (We might represent the two word types in writing as "home" and "h-o-m-e" if we wish.)
A language provides a mechanism for classifying linguistic tokens under linguistic types. There are very few restrictions on how the classification scheme can work, except contingent ones derived from our recognitional abilities. Imperceptible differences between tokens will not do the job.
It is quite possible, then, to have a language where the classification system is time-dependent. Thus, "home" at odd-numbered hours of the day means a tank, and at even-numbered hours it means an F-16. There are, thus, two word-types with the same phonemes, and to distinguish between them you have to check what time it is. Such a language might well be useful for confusing an evesdropping enemy.[note 1]
Imagine now a language L1 where the sound "chow" when uttered at a time t denotes the time equal to t+7minutes, when t is during an even-numbered hour, and denotes the time equal to t-7minutes, when t is during an odd-numbered hour, and where the type of the word is identified by both the sound "chow" and the time of utterance. This language can be understood as containing continuum many word-types, identified partly by the time at which the word-type is tokened and partly by the phonemes. This is a very odd language, but a possible one.
Observe that in L1 no utterance of "chow" is the utterance of an indexical. What an indexical refers to depends on both the token's type and on the context of utterance. But what "chow" refers to does not depend on the context of utterance, but only on the token's type. The token's type depends on the time of utterance, but that is a different matter.
Consider now a language L2 where the sound "fow" when uttered at a time t denotes the time t, and where the type of the word is identified by both the sound "fow" and the time of utterance. Just as no utterance of "chow" in L1 was an indexical, so no utterance of "fow" in L2 is an indexical. Rather, it is the utterance of a fine, upstanding, context-free referring term.
But now a question: How do we know that utterances of "now" in English are utterances of an indexical? Why not analyze utterances of "now" in English precisely the way utterances of "fow" are to be analyzed in L2? There are, I submit, no facts of linguistic practice (normative or not) that allow us to distinguish between English's "now" and L2's "fow". If linguistic facts supervene on facts of linguistic practice, there is no fact of the matter whether an utterance of "now" should be read as an indexical whose type is identified by the phonemes or as a non-indexical whose type is partly identified by the phonemes and partly by the time of utterance.
If we understand "now" along the lines of "fow", then any argument for the A-Theory of time based on our use of "now" is likely going to fail. For "fow" is perfectly at home in the eternalist world of the B-Theory. And what I said about "now" goes for tenses as well.
This strategy is closely parallel to the old failed B-theoretic attempt to translate "now" into the time of utterance. That attempt failed because when one translated "It is now 11:56 am", it translated into "It is 11:56 am at 11:55 am", and hence a sentence that one could reasonably be wrong about got translated into one that no one could be reasonably wrong about, which is absurd. On the present strategy, an utterance of "now" at 11:56 am does refer to the 11:56 am, indeed is rather like a proper name for it. In a sense "It is now 11:56 am" may be a tautology, but it is not a trivial tautology. Rather, it is like "Cicero is Tully" or "London is Londres."
If all this is right, then no deep facts about language hang on the distinction between indexicals and non-indexicals. There may be more than one way of classifying bits of utterances into types, and for any way of classifying that makes a bit of utterance into a token of an indexical, there is a way of classifying that makes that bit of utterance into a token of a non-indexical identified in some non-phonemic way. Each classification should give rise to the same proposition as expressed by the utterance as a whole.