Hey @brend_a_rv01, thanks for reaching out to the Community!
If you redeem a Gift Card today, you'll be able to use your Premium subscription right away. For example, if you redeem the gift card today (15/09/19) you'll be able to use the subscription until (15/10/19).
And yes, you can redeem two Gift Cards in the same day. You can redeem them here.
I hope this helps!
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Note: I'm not a Spotify employee.