Hi @Anonymous User
With a one day or one week sports pass you can save on your account for about 365 days if you wish.
What the now tv system doesn't allow is to have two sports passes on your account at the same time (either saved or active) unless it is a Mobile Sports pass with another full blown sports pass.
If you are going to buy a further one month sports pass (once your day pass has finished) then look at buying the one month £16.99 Christmas deal offer via the nowtv offers webpage linked below.
https://w ww.nowtv.com/offers
Once your day pass is up, you should be eligible for the £16.99 one month offer.
Just be aware that NowTV month passes are not automatically self cancelling and you need to cancel the one month pass yourself if you don't want to continue with the service in the future.