I think the wording of the patter needs fair a bit of refinement. More short, snappy phrases would go some way towards making it sound more dramatic.
But on a more fundamental level, your terminology is wrong. The effect has nothing to do with time
travel as the term is generally understood. If you sent a pack of cards back in time, then the pack of cards arriving from the future would first pop into existence, and then the original pack would pop out of existence (i.e. vanish) as it is sent back to the past. In between, you would have two packs of cards. No, by all the conventions of science fiction, this is not time travel at all but rather time
erasure. What you're doing is deleting a few seconds of the pack's history so that it is as though those seconds never existed. Time erasure is not as common in science fiction as time travel, but it does crop up from time to time (ahem). One fairly common use for it is as a method of execution in which the criminal's entire life is deleted from history.
When I was watching the first part of the trick, one of my thoughts was that turning one of the
cards around in order to represent the rewinding of the pack's history doesn't make any sense at all. And indeed it doesn't, but the spectator does need something visual to associate with the rewinding of time. It occured to me that you could rewind the pack's history by means of a tap wrench like this.
You could place the pack on a table, then hold the tap wrench on the cards, and then turn the handle and erase five ... ten ... fifteen seconds of the pack's history. But for the second part of the trick, with the colour change, the tap wrench idea obviously won't work. I still think it would improve the first half, but then afterwards you would need to explain that you can actually do it with mental energy alone although it is rather exhausting.
But you know what, for the second part of the trick it also doesn't work particularly well to rewind time by a specified number of seconds as you do. The problem is that there never WAS a moment in time at which the four was face-up on top of the deck and the queen was sticking out of the middle, face-down. So how can you send the deck of cards back to a moment in its history that never occured in the first place?
To make the effect work in a way that is consistent with the time manipulation premise, you need to at some point have the cards arranged as near as possible to EXACTLY the way they will look immediately after the colour change. That is, the queen is sticking out the middle and the four is being held face-up just above the pack. At that point, inform the spectator that right now is the moment in the history of the cards to which you will send them back.
I tend to agree with Michael that the third and final segment of the trick is an anti-climax. But imagine you liked my idea of using a tap wrench for the first part. Then you now have a tap wrench in which fifteen seconds of time is stored. What happens when those fifteen seconds are discharged? I imagine that it would make some object suddenly become fifteen seconds older (i.e. time is accelerated). What magical effect could you use to demonstrate this? I don't know, but it's something to think about.
Edit: I don't know how much science fiction or fantasy you read, but you would do well to immerse yourself in the literature for research purposes. For a start, there are some bits in Terry Pratchett's "Thief of Time" that might be useful as a tool to help you think about the possibilities of time manipulation.