Thanks for the question! It's one that a lot of people ask us, so I appreciate the chance to reply.
No, you don’t have to listen to both at the same time. Listening to just one of the tracks, once a day should be very effective.... whatever makes the most sense to you, time-wise, is a good rule of thumb, because then you’re more likely to follow through.
If you only have 20 minutes, listen to just one of them. If you're more likely to listen to both if you do it all at once, and you've got the time, then by all means, listen to both.
If you're in a position to spread it out during the day – say, play the imagery in the morning and the affirmations in the afternoon, that would be extremely effective.
And if you have only time for one and you respond equally well to both, listen to the imagery. It gets you into a more immersive, altered state, so you’ll be all the more receptive to the content.
But if imagery makes you fidgety, the affirmations will be absolutely fine for you to use instead.
And if you’ve only got 10 minutes, listening to anything for 10 minutes is a whole lot better than listening to nothing. So do what you can. Convenience is important, as is natural preference, because you want to stack the deck in favor of your doing this as often as you can.
I hope that clarifies your question. Let me know if it didn't.