IMHO, the 2nd D+ coupon discount can be used towards the remaining days of internet package.
Another scenario, with one device on at any given time, is to skip the first day as it's only 6-7 hours depending on when you depart. Then use the 1st D+ coupon for day 2 & 3, follow that with the 2nd D+ coupon and it cover day 4 & 5 and then purchase the rest of the days in internet package. Based on the per day cost of $24.99 on my December 4th Oasis sail, the bottom line estimated at around $50 ($24.99 x 2)