On straggler backers: it's completely normal. Don't worry!
Not all backers will answer your survey right away, but typically, the majority of your backers will fill out their surveys 3-7 days after the initial time you send out your surveys.
In the world of crowdfunding, it's completely normal to have "straggler backers"—backers who may not immediately fill out their survey even a year or three from now—trust us, we know from experience!
Straggler backers will always trickle in, but our advice would be to first focus on delivering the initial group of backers who have given you the necessary survey information, and make that group of backers happy. If you can deliver on these backers, you'll have run a successful campaign!