You can still get the final reward if you cannot unlock the Bounty Mission on time. If I'm not wrong, every time you open a new day for the said event, you will get a free 1 Pet Fiesta Token. Considering you only need 35 to get the final reward, you would need to finish all the remaining 6 missions. So basically, for each mission given per day, you would receive a total of 6 Pet Fiesta Tokens(x1 when you unlock to see the quest, x5 when you finish all 5 quests for that specific day). Though just to be sure, much better if you can progress faster with your Main Quest, given that there's a Server Hot Time Event going on right now.