The update notes say that you will receive the following rewards, followed with the aforementioned list, implying you'll receive all of them. The notice above says otherwise.

http://maplestory.nexon.net/news/updates/update-notes/00IcV#hottime

Update Notes (emphasis mine) Wrote:Read complete details about how the Hot Time event works here.

July 25 at 2:30 PM Pacific (5:30 PM Eastern)
Requirement: Lv. 30 to receive and open the gift box
One gift box per account.
You must be logged in at or before 2:30 PM Pacific (5:30 PM Eastern) on July 25, 2015, and then stay logged in for at least one minute following the appointed time (2:31 PM PDT / 5:31 PM EDT) to receive a reward. We recommend you log in a few minutes in advance to make sure you don’t miss it!
If you have a full inventory when the Hot Time occurs, you are able to speak with Cassandra until 11 PM Pacific on July 25 (2 AM Eastern on July 26) to receive the reward.
The Hot Time box can be opened after 3 PM Pacific (6 PM Eastern).
The gift box will disappear if unopened by 11:59 PM Pacific on July 25 (2:59 AM Eastern on July 26).
Please note: to ensure you receive the Hot Time box, make sure you are in a Major Town (such as Henesys, Leafre, Orbis, etc.), not in the Cash Shop, Star Planet, Cross World PQ, Boss Arena, etc.
Rewards: You will receive the following rewards.
Epic Potential Scroll 100%: Expires 7 days after obtaining from reward box
Character Slot Expansion Coupon: Expires 7 days after obtaining from reward box
Spell Trace (1000)
FIREPOWER Coin Coupon: Expires 7 days after obtaining from reward box
Summer Hair Coupon: Expires 7 days after obtaining from reward box
Golden Hammer 100%: Expires 7 days after obtaining from reward box

The Reward Box also has a chance to give you one extra special item from the following rewards.
I'm a Lucky Guy Medal: Untradeable
Passion Badge : Untradeable
RED Weapon Box : Untradeable, Expires 7 days after obtaining from reward box
Tyrant Cape Exchange Box : Untradeable, Expires 7 days after obtaining from reward box
Twinkle Star Package Coupon : Untradeable
100,000 Maple Point Coupon: Untradeable
Unique Potential Scroll 50%: Can be shared within the account